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What is Breast Density, Why Does It Matter?

1. What are dense breasts? Does it have something to do with the look/feel of breasts?X

All breasts contain glands, fibrous tissue, and fat. Dense tissue is made of glands and fibrous tissue (referred to as "fibroglandular" tissue). Dense tissue blocks x-rays and therefore shows up white on a mammogram. Fatty tissue allows more x-rays to penetrate and therefore shows up as black or dark gray on a mammogram. Each woman's breasts are different than the next and contain a unique mix of fatty and dense tissue. Some women's breasts are almost all fat, some have very little fat, and some are in between. Dense breasts are normal and tend to become less dense with age and menopause. Breast density is not determined by how a breast looks or feels. The radiologist can determine the breast density by examining the images from a mammogram.

Figure A. Courtesy of Jeremy M. Berg. Ph. D. Figure B.

Diagrams of the normal breast. A) The normal breast is composed of milk-producing glands at the ends of ducts leading to the nipple. There is layer of fat just beneath the skin. Often a few lymph nodes are seen near the underarm (axilla). B) On a mammogram, fat appears dark gray, and glandular tissue, fibrous tissue, muscle, and lymph nodes appear light gray or white. Masses due to cancer also appear white.

2. Are lumpy breasts or fibrocystic breasts the same as dense breasts? X

Having "lumpy" breasts doesn't mean a patient has dense breasts, nor does it mean the breasts have fibrocystic changes. Both fatty and dense breasts can feel lumpy as the ligaments that support the breast can surround fat lobules and make them feel almost like soft grapes.

A fibrocystic breast is not the same as a dense breast. Fibrocystic change is a hormonal condition that is most pronounced when women are young and usually decreases after menopause. Fibrocystic breasts can appear dense due to cysts and/or areas of fibrosis (which resemble scar tissue). Cysts are very common and do not increase the risk for breast cancer; however, some other fibrocystic changes indicate active areas ("proliferative changes") in the breast which do slightly increase risk for breast cancer English | Spanish .

3. How is breast density determined?X

A woman's breast density is usually determined during her mammogram by her radiologist by visual evaluation of the images taken. Breast density can also be measured from mammograms by computer software and it can be estimated on computed tomography (CT scan) and MRI imaging. In the U.S., information about breast density is usually included in a report sent from radiologist to the referring doctor after a mammogram. Breast density information may also be included in the patient letter sent after their mammogram. In Europe, national reporting guidelines to physicians vary; no country has a public policy for density reporting to patients.

A woman's breast tissue is categorized as one of four BI-RADS®i categories:

Mammographic images representative of the four categories of breast density:
(A) Fatty; (B) Scattered fibroglandular tissue; (C) Heterogeneously dense; (D) Extremely dense
Breasts which are (C) heterogeneously dense, or (D) extremely dense, are considered "dense breasts."

A. ALMOST ENTIRELY FATTY – On a mammogram, most of the tissue appears dark gray or black while small amounts of dense (or fibroglandular) tissue display as light grey or white.
About 10% of all women have breasts considered to be "fatty."

B. SCATTERED FIBROGLANDULAR DENSITY – There are scattered areas of dense (fibroglandular) tissue mixed with fat. Even in breasts with scattered areas of breast tissue, cancers can sometimes be missed when they look like areas of normal tissue or are within an area of denser tissue.
About 40% of all women have breasts with scattered fibroglandular tissue.

C. HETEROGENEOUSLY DENSE – There are large portions of the breast where dense (fibroglandular) tissue could hide masses.
About 40% of all women have heterogeneously dense breasts.

D. EXTREMELY DENSE – Most of the breast appears to consist of dense (fibroglandular) tissue creating a "white out" situation, making it extremely difficult to see through.
About 10% of all women have extremely dense breasts.

iSickles EA, D'Orsi CJ, Bassett LW, et al. ACR BI-RADS Mammography. ACR BI-RADS Atlas, Breast Imaging Reporting and Data System. Reston, VA: American College of Radiology, 2013.

4. Why does breast density matter on a mammogram?X

Cancers can be hidden or "masked" by dense tissue. On a mammogram, cancer is white. Normal dense tissue also appears white. If a cancer develops in an area of normal dense tissue, it can be harder or sometimes impossible to see it on the mammogram, like trying to see a snowman in a blizzard. If a cancer (white) develops in an area of fat (black or dark gray), it is usually easier to detect even when it is small. Because dense tissue can hide cancers, the more fatty a breast is, the more effective the mammogram is in showing the cancer. As breast density increases, the ability to see cancer on mammography decreases. The images below are examples of how cancer presents in each breast density category:

Courtesy of Dr. Regina Hooley

Mammographic Images Showing How Cancer Looks in Each of the Breast Density Categories. A) A small cancer (arrow) is easily seen in a fatty breast. B) In this breast with scattered fibroglandular density, a large cancer is easily seen (arrow) in the relatively fatty portion of the breast, though a small cancer could have been hidden by areas of normal dense tissue. C) In this heterogeneously dense breast, a 4 cm cancer (arrows) is hidden by the dense breast tissue. Note the metastatic node in the left axilla (curved arrow). D) In this extremely dense breast, a cancer is seen because part of it is located in the back of the breast where there is a small amount of dark fat making it easier to see (arrow and triangle marker indicating lump). If this cancer had been located near the nipple and completely surrounded by white (dense) tissue, it probably would not have been seen on mammography.

5. Do dense breasts affect the risk of developing breast cancer?X

Yes. Higher breast density is a risk factor for the development of breast cancer. According to the American Cancer Society's Breast Cancer Facts & Figures 2013-2014, "The risk of breast cancer increases with increasing breast density; women with very high breast density have a 4- to 6-fold increased risk of breast cancer compared to women with the least dense breasts."i,ii,v

There are probably several reasons that dense tissue increases risk. One is that the glands tend to be made up of relatively actively dividing cells which can mutate and become cancerous: the more glandular tissue, the greater the risk. The second is that the local environment around the glands may produce certain growth hormones that stimulate cells to divide, and this seems to be more true for fibrous breast tissue which is dense, than for fatty breast tissue.

Most women have breast density somewhere in the middle range, with their risk for developing breast cancer in between those with extremely dense breasts and those with fatty breasts.iii Risk for developing breast cancer is influenced by a combination of many different factors including age, family history of cancer (particularly breast and/or ovarian cancer), and prior atypical breast biopsies. Most women who develop breast cancer have no additional risk factors other than being female and aging.

Some risk factors can be influenced by behavior. Alcohol intake increases the risk of developing breast cancer, and the greater the intake, the greater the risk. Being overweight, especially after menopause, also increases the risk for breast cancer. Regular exercise reduces the risk of breast cancer.

There is currently no reliable way to fully know the interplay of breast density, family history, prior biopsy results, and other factors in determining overall risk English | Spanish . However, the largest studyiv of its kind found that dense breast tissue increases the risk of developing breast cancer more than family history, postmenopausal weight gain, or late childbearing.

For live breast cancer risk assessment tools click HERE.

iAmerican Cancer Society. Breast Cancer Facts & Figures 2013-2014. Atlanta: American Cancer Society, Inc. 2013. Retrieved from: http://www.cancer.org/acs/groups/content/@research/documents/document/acspc-042725.pdf

iiHarvey JA, Bovbjerg VE. Quantitative assessment of mammographic breast density: relationship with breast cancer risk. Radiology 2004; 230:29-41

iiiKerlikowske K, Cook AJ, Buist DS, et al. Breast cancer risk by breast density, menopause, and postmenopausal hormone therapy use. J Clin Oncol 2010; 28:3830-3837

ivEngmann NJ, Golmakani MK, Miglioretti DL, Sprague BL, Kerlikowske K, for the Breast Cancer Surveillance Consortium. Population-Attributable Risk Proportion of Clinical Risk Factors for Breast Cancer. JAMA Oncol.Published online February 02, 2017. doi:10.1001/jamaoncol.2016.6326

vMcCormack VA, dos Santos Silva I. Breast density and parenchymal patterns as markers of breast cancer risk: a meta-analysis. Cancer Epidemiol Biomarkers Prev. 2006;15(6):1159-69.

6. How does breast density compare to other risk factors?X

The charts below detail relative risk and prevalence

Relative Risk: The top chart shows approximate relative risk of developing invasive breast cancer by age 80 for a woman with a given risk factor compared to a woman without that risk factor: disease-causing BRCA1 or -2 mutation; prior ductal carcinoma in situ; prior atypical ductal hyperplasia; first-degree relative (mother or sister) diagnosed with breast cancer by age 50; combined estrogen and progesterone therapy after menopause; heterogeneously dense breast tissue (relative to a woman with fatty breasts); extremely dense breast tissue (relative to a woman with fatty breasts).

Percent Affected: The lower chart shows estimated prevalence of each risk factor in American women aged 40-74, except for hormone replacement therapy which applies only to postmenopausal women. Dense breast tissue is quite common, seen in 43% of all women aged 40-74. Charts courtesy Dr. Emily Conant

Cummings SR, Tice JA, Bauer S ,et al. Prevention of breast cancer in postmenopausal women: approaches to estimating and reducing risk..J Natl Cancer Inst 2009;101:384–398

Couch FJ,. DeShano ML, Blackwood MA, et al. BRCA1 Mutations in Women Attending Clinics That Evaluate the Risk of Breast Cancer N Engl J Med 1997; 336:1409-1415May 15, 1997DOI: 10.1056/NEJM199705153362002

Sprague BL Gangnon RE Burt V, et al. Prevalence of mammographically dense breasts in the United States. J Natl Cancer Inst. 2014 Sep 12;106(10). pii: dju255. doi: 10.1093/jnci/dju255.

What do I need to know about dense breasts?

7. Are screening mammography outcomes different for dense breasts vs. fatty breasts?X

Yes. Because cancer is more often missed on mammograms in women with dense breasts, it is more often found as a lump or because of other breast symptoms in the interval between screens (i.e. "interval cancer," see Table 1). Such interval cancers tend to be more aggressive with worse outcomes. Cancers found in dense breasts are more often advanced (stage IIb and III), are more often multifocal or multicentric, and a mastectomy is more often needed for treatment.i Dense breasts also increase the risk of recurrence in women with a history of breast cancer (if patient has not had radiation).

iArora N, King TA, Jacks LM, et al. Impact of breast density on the presenting features of malignancy. Ann Surg Oncol 2010; 17 Suppl 3:211-218

Table 1. Interval Cancers and Breast Density

Visually Estimated Breast Density

Odds Ratio of Interval Cancer (95% Confidence Interval)

< 10%


10 to 24%

2.1 (0.9 to 5.2)

25 to 49%

3.6 (1.5 to 8.7)

50 to 74%

5.6 (2.1 to 15.3)

≥ 75%

17.8 (4.8 to 65.9)

From Boyd NF, et al. NEJM 2007;356:227-36

8. Is it unusual to have dense breasts?X

No. Dense breasts are neither unusual nor abnormal. By age:

  • More than half of women under the age of 50 have dense breasts
  • About 40 percent of women in their 50s have dense breasts
  • About 25 percent of women age 60 and older have dense breastsi

Generally, glandular tissue (which contributes to breast density) tends to shrink after menopause so that sometimes the breasts will appear less dense on mammograms as a woman gets older. However, many women continue to have dense breast tissue after menopause. During pregnancy and breastfeeding, the dense tissue grows and the breasts become denser and often larger.

The tissue composition of every breast is different (and can differ during a woman's own lifetime) which is why women should know their own breast density and understand the limitations of mammography for their breast type.

iKerlikowske K, Ichikawa L, Miglioretti DL, et al. Longitudinal measurement of clinical mammographic breast density to improve estimation of breast cancer risk. J Natl Cancer Inst 2007; 99:386-395

iSprague BL, Gangnon RE, Burt V, et al. Prevalence of mammographically dense breasts in the United States. J Natl Cancer Inst 2014; 106

9. Is breast size related to breast density?X

Smaller breasts tend to be dense, and large breasts are more often relatively fatty, but there is wide variation at the individual level.

10. If a woman has dense breasts, will she always? X

Breasts tend to become less dense as women get older (see Figure below), especially after menopause as the glandular tissue atrophies and the breast may appear more fatty replaced. Taking hormones for menopausal symptoms can delay the regression of dense tissue. If a patient loses a lot of weight, her breasts may appear denser due to the relative loss of fat. There is also variability in the visual assessment of breast density so that the density reported in the mammogram might be "scattered" one year and "heterogeneously dense" the next year or vice versa without any true change in breast density. In both situations, there are areas within the breast where there is some dense tissue which could mask cancer detection. In recent years, the use of automated computer-based density assessment can provide reproducible and objective quantification of breast density, avoiding interobserver variability.i

iDestounis, S, et al. Qualitative Versus Quantitative Mammographic Breast Density Assessment: Applications for the US and Abroad. Diagnostics (Basel) 2017; 7: 30, epub May 31, 2017.


Courtesy of Dr. Wendie Berg

11. If a woman does not have dense breasts, what should she do?X

Annual mammography (with tomosynthesis if available) is recommended if she is over the age of 40 and in good health. If the patient is at high risk of developing breast cancer, she may be recommended to have an MRI every year in addition to mammography.

12. Does having dense breasts increase the chance of dying from breast cancer?X

Though there is not extensive research on this topic, one studyi indicated that because women with dense breasts are at a greater risk of developing breast cancer, their risk of dying from breast cancer is about double that of the general population. Two other studies evaluated women with breast cancer and found an increased risk of death among women with fatty breasts; the reasons for this are not well understood.ii A recent analysis from The Netherlands showed a smaller estimated mortality reduction from screening mammography of 13% in women with dense breasts compared to 41% in women with fatty breasts. Reduced benefit from mammographic screening is attributed to the masking effect of dense tissue with tumors detected later, when they were larger, in women with dense breasts.iii

i Chiu, S, Duffy, S, Yen, A, et al. (2010). Effect of baseline breast density on breast cancer incidence, stage, mortality, and screening parameters: 25-year follow-up of a Swedish mammographic screening. Cancer Epidemiology, Biomarkers and Prevention (19): 1219. Retrieved http://cebp.aacrjournals.org/content/19/5/1219.short

ii Gierach, GL, Ichikawa, L, Kerlikowske, K, et al. (2012). Relationship between mammographic density and breast cancer death in the breast cancer surveillance consortium. Oxford University Press. DOI:10.1093/jnci/djs327

ii Masarwah, A. Auvinen, P, Sudah, M, et al. (2015). Very low mammographic breast density predicts poorer outcome in patients with invasive breast cancer. European Society of Radiology. DOI 10.1007/s00330-015-3626-2

iii van der Waal D, Ripping TM, Verbeek AL, Broeders MJ. Breast cancer screening effect across breast density strata: A case-control study. Int J Cancer. 2016.

Mammograms and Dense Breasts:

13. If a mammography report indicates the patient has heterogeneously dense or extremely dense tissue but is otherwise categorized as "negative" or "benign" what should be considered next? X

Dense breasts are "normal." In fact, 40% of women over age 40 have dense breasts. But dense breast tissue can hide cancer on a mammogram and can reduce the effectiveness of mammography screening. So a "normal," "negative," or "benign" mammogram result does not reliably exclude cancer in women with dense breasts. This is why, sometimes, a woman with dense breasts may have cancer detected soon after a "normal," "negative," or "benign" mammogram. This is known as an "interval cancer."

14. A patient recently had a "normal" mammogram and has extremely dense breasts. She now feels a lump. What should you recommend?X

It is important for any woman not to ignore a lump just because the recent mammogram was normal, and this is especially important if the breasts are dense. While cysts, other benign masses, and areas of normal tissue can present as lumps, malignant masses, especially those lacking calcifications, are frequently masked by dense breast tissue and a "normal" "negative" or "benign" mammogram does not mean that there is no cancer present. Tomosynthesis can help show some cancers not found with 2D-mammography, but ultrasound is the test of choice to evaluate palpable lumps and allows targeted assessment and correlation of the area being felt with findings on ultrasound. If there is a mass suspicious for cancer, the radiologist/technologist may also include ultrasound of the tissue in the axilla (under the arm) because the first place cancer will spread is to lymph nodes in the axilla. Cancers presenting because of symptoms prior to the next annual mammogram are called "interval cancers" and interval cancers are increasingly common with increasing breast density.

15. When should screening mammography begin and stop?X

Based on randomized trials (invitation to screening) mammography, there is at least a 15% decrease in deaths due to breast cancer in women screened in their 40's and a 22% reduction in deaths among women screened from ages 50 to 74.i In observational studies of women actually having mammographic screening, reduction in deaths due to breast cancer is closer to 40%.ii,iii Based on these results, the American College of Radiology (ACR) recommends annual screening beginning at age 40 for women at average risk for breast cancer.iv The European Society of Breast Imaging (EUSOBI) recommends biennial screening mammography for average-risk women aged 50–69 years; extension up to 73 or 75 years biennially and from 40–45 to 49 years, annually.v Breast cancer incidence peaks earlier, in the 40s, for African American, Asian, and Hispanic women,vi than for Caucasian women where the peak is in the early 50s. As such, it is especially important for African American, Asian, and Hispanic women to start screening by age 40. The age to stop should be based on a woman’s overall health status. Women with a life expectancy less than 5-7 years are unlikely to realize a benefit from screening mammography.

Women at high risk for breast cancer because of known or suspected disease-causing mutations in BRCA or other genes such as P53 should begin screening earlier and American Cancer Society recommendations, as well as those of the European Society of Mastology (EUSOMA), include annual MRIvii, viii: BRCA-1 carriers should begin by age 25, and BRCA-2 carriers by age 30. Women with a history of radiation therapy to the chest (e.g. for Hodgkin’s disease) before age 30 should begin screening with mammography and MRI at age 25 or 8 years after treatment, whichever is later. Emerging evidence suggests that for BRCA-1 carriers who have annual MRI, the benefit of mammography is relatively small before age 40.ix Once a woman has had breast cancer, she should have at least annual mammography; if she also has dense breasts and/or was diagnosed with breast cancer by the age of 50, the ACR recommends she consider annual MRI in addition to mammography.x

For other women with a family history of breast cancer, it is important to consider many factors, including the age at diagnosis of family members. Several risk models have been developed. While all models can over- or underestimate risk in a given individual, the Tyrer-Cuzick model is the most consistently accurate and, as of September 2017, includes breast density as a risk factor. For women estimated to have a lifetime risk of breast cancer of 20% or more, annual MRI screening has been recommended in addition to mammography.vii,x

i Nelson HD, Tyne K, Naik A, Bougatsos C, Chan BK, Humphrey L. Screening for breast cancer: an update for the U.S. Preventive Services Task Force. Ann Intern Med 2009; 151:727-737, W237-742

ii Coldman A, Phillips N, Wilson C, et al. Pan-canadian study of mammography screening and mortality from breast cancer. J Natl Cancer Inst. 2014;106(11).

iii Broeders M, Moss S, Nystrom L, et al. The impact of mammographic screening on breast cancer mortality in Europe: a review of observational studies. J Med Screen. 2012;19 Suppl 1:14-25.

iv Monticciolo DL, Newell MS, Hendrick RE, et al. Breast Cancer Screening for Average-Risk Women: Recommendations From the ACR Commission on Breast Imaging. J Am Coll Radiol. 2017;14(9):1137-43

v Sardanelli F, Aase HS, Alvarez M et al. Position paper on screening for breast cancer by the European Society of Breast Imaging (EUSOBI) and 30 national breast radiology bodies from Austria, Belgium, Bosnia and Herzegovina, Bulgaria, Croatia, Czech Republic, Denmark, Estonia, Finland, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Israel, Lithuania, Moldova, The Netherlands, Norway, Poland, Portugal, Romania, Serbia, Slovakia, Spain, Sweden, Switzerland and Turkey. Eur Radiol. 2017; 27:2737-2743.

vi Stapleton SM, Oseni TO, Bababekov YJ, Hung YC, Chang DC. Race/Ethnicity and Age Distribution of Breast Cancer Diagnosis in the United States. JAMA Surg. 2018.

vii Saslow D, Boetes C, Burke W, et al. American cancer society guidelines for breast screening with MRI as an adjunct to mammography. CA Cancer J Clin 2007; 57:75-89

viii Sardanelli F, Boetes C, Borisch B et al Magnetic resonance imaging of the breast: recommendations from the EUSOMA working group. Eur J Cancer 2010; 46(8):1296– 1316

ix Heijnsdijk EA, Warner E, Gilbert FJ, et al. Differences in natural history between breast cancers in BRCA1 and BRCA2 mutation carriers and effects of MRI screening-MRISC, MARIBS, and Canadian studies combined. Cancer Epidemiol Biomarkers Prev. 2012;21(9):1458-68.

x Monticciolo DL, Newell MS, Moy L, Niell B, Monsees B, Sickles EA. Breast Cancer Screening in Women at Higher-Than-Average Risk: Recommendations From the ACR. J Am Coll Radiol. 2018;15(3 Pt A):408-14.

16. Should women with dense breasts still have mammography screening?X

Yes. Mammography is the first step in screening for most women. While additional screening may be recommended for women with dense breasts and/or high risk for developing breast cancer, there are still some cancers and precancerous changes that will show on a mammogram better than on ultrasound or MRI. Wherever possible, women with dense breasts should have digital mammography rather than film mammography, and preferably with DBT (tomosynthesis) due to slightly improved cancer detection using digital mammography.i About half of cancers seen on mammography have calcifications (white dots that are like salt crystals), and calcifications can be seen even in dense areas of the breast. It is important to know that at least a few calcifications can be seen in nearly all breasts and that the vast majority of calcifications seen on a mammogram are not due to cancer. Some calcifications require special magnification mammography views to be adequately evaluated. A biopsy may be recommended for calcifications which are new or increasing and have a concerning appearance on magnification views. Even when a biopsy is recommended for calcifications, only about 1 in 4 or 5 are shown to be due to cancer. When there are no calcifications, some masses due to cancer can be seen in dense breasts because they distort (pucker) the tissue around them. Some masses due to cancer are seen in dense breasts because at least a portion of the mass is in an area where the breast is more fatty.

Women who are pregnant may want to defer screening mammography until after the pregnancy. (For women who are pregnant with a lump or other breast problem, diagnostic ultrasound is performed first, and mammography can be used safely and effectively performed if needed with abdominal shield protection.) For women who are breastfeeding, if they will only be nursing for a short time (3-5 months), they might defer screening mammography until 2-3 months after the baby is weaned. For those planning on breastfeeding 6 months or longer, mammography screening can be performed while nursing but probably best to schedule it after the first 3 months when the breasts are less likely to be engorged. Patients who are breastfeeding will almost certainly have dense breasts during that time.

iPisano ED, Gatsonis C, Hendrick E, et al. Diagnostic performance of digital versus film mammography for breast-cancer screening. N Engl J Med 2005; 353:1773-1783

Courtesy of Dr. Wendie Berg

Mammography Shows Some Early Breast Cancers not seen on Ultrasound. Magnification mammographic images of heterogeneously dense breasts show new grouped calcifications (white specks that are like salt crystals within yellow circles). These are difficult or impossible to see with ultrasound. Most calcifications seen on mammograms are not due to cancer; however, biopsy showed these to be due to ductal carcinoma in situ (DCIS), a noninvasive cancerous change which, if left untreated, can progress to invasive breast cancer.

17. If a woman is a breast cancer survivor and has dense breasts, is mammography adequate screening?X

Because many studies have shown improved detection of early, node-negative cancers with MRI even after normal mammography and ultrasound, the ACR now recommendsi annual MRI in addition to mammography (either 2D or 3D) for the following women (provided the patient has not had bilateral mastectomy):

  • All women with a personal history of breast cancer and dense breasts.
  • Women with any breast density diagnosed with breast cancer by age 50.

One study from UC San Franciscoii found that screening mammography every 6 months instead of every year improved early detection, but this is not routinely recommended. Tomosynthesis, or 3D mammography, improves cancer detection in most women (by 1-2 per 1000 screening examinations) compared to standard 2D mammography. In women with extremely dense breasts, however, tomosynthesis remains limited as cancers that lack calcifications can remain masked by overlying tissue. For women with dense breasts and prior breast cancer, screening ultrasound can be added to annual mammography, though the added cancer detection (at 2-4 per 1000 examinations) is less than that achieved with MRI (at 7-20 per 1000 examinations). Indeed, MRI is more effective at depicting early cancer in women of any breast density, even after a normal mammogram.

If MRI is performed, screening ultrasound is of no benefit. Women with a personal history of breast cancer and dense breasts who are unable to tolerate MRI may consider screening ultrasound in addition to mammography.

iMonticciolo DL, Newell MS, Moy L, Niell B, Monsees B, Sickles EA. Breast Cancer Screening in Women at Higher-Than-Average Risk: Recommendations From the ACR. J Am Coll Radiol. 2018;15(3 Pt A):408-14.

iiArasu VA, Joe BN, Lvoff NM, et al. Benefit of semiannual ipsilateral mammographic surveillance following breast conservation therapy. Radiology. 2012;264(2):371-7.

18. Are a digital mammogram and a 3D mammogram (known as tomosynthesis) the same thing?X

No, but they are different types of mammograms. Both involve computer-generated images. A standard 2D digital mammogram captures images from two different angles (or views). Tomosynthesis (3D) captures images from many different angles (projection images). The multiple images are then compiled by a computer and used to create thin "slice" images of a breast. A "3D" mammogram can be performed in addition to a standard 2D mammogram. Tomosynthesis uses x-rays that produce about the same radiation exposure to the breasts as a standard mammogram: if a patient has both 2D and 3D their breasts will receive nearly twice the amount of radiation as from a standard mammogram, though the combined dose is still within standard safety limits. A new technique that creates a 2D-like image from the projection images, i.e. a "synthetic" 2D image, is being used in many centers instead of the standard 2D mammogram. The total radiation dose from tomosynthesis with synthetic 2D images is similar to or slightly more than a standard 2D mammogram and varies with the breast thickness and tissue density.

19. Is the mammography recall rate (or the false positive rate/false alarm rate) higher for women with dense breasts than in women with fatty breasts?X

Yes. Women with dense breasts are about twice as likely to be called back for additional testing as are women with non-dense breasts, and the vast majority (about 95%) of callbacks will not show cancer.i Thus, the denser the breast, the more likely a false positive (additional testing when no cancer is present) is to occur. Women with extremely dense breasts are about twice as likely to experience a false positive as are women with fatty breasts.

iMcCarthy, AM, Kontos, D, Synnestvedt, M, et al. (2014). Screening outcomes following implementation of digital breast tomosynthesis in a general-population screening program. JNCI 106(11).

iLehman, CD, White, E, Peacock, S, et al. (1999). Effect of age and breast density on screening mammograms with false-positive findings. AJR 173(6):1651-1655. Reference: http://www.ncbi.nlm.nih.gov/pubmed/10584815

20. Is annual screening more effective than biennial screening?X

Yes. If a woman is going to participate in screening, annual screening is especially important for women in their 40s when cancers tend to be more biologically aggressive. Greater breast density also contributes to worse outcomes from screening mammography among women in their 40s.i Biennial screening is nearly as effective as annual screening at reducing deaths due to breast cancer among women who are over the age of 50 (or postmenopausal).

i Hendrick RE, Helvie MA, Hardesty LA. Implications of CISNET modeling on number needed to screen and mortality reduction with digital mammography in women 40-49 years old.AJR American journal of roentgenology 2014; 203:1379-1381

i Bailey SL, Sigal BM, Plevritis SK. A simulation model investigating the impact of tumor volume doubling time and mammographic tumor detectability on screening outcomes in women aged 40-49 years. J Natl Cancer Inst 2010; 102:1263-1271

21. Are there some cancers found by screening mammography which do not require treatment?X

Probably, but it is difficult to determine this at the individual level, i.e. for a given patient. Some cancers are so indolent and slow-growing that they might not ever have been detected otherwise in a patient's lifetime ("overdiagnosis"). While estimates of overdiagnosis vary, on average, of 11 breast cancers found with screening, 2 will be life saving, 1 will represent overdiagnosis, and 8 will be found earlier than they would have been without screening (with better prognosis).i Some ductal carcinoma in situ found on the first screening examination represents overdiagnosis (estimated at 37% of such cases) but new findings on subsequent screens are uncommonly overdiagnosis (estimated at 4% of cancers on annual screens).

iYen MF, Tabar L, Vitak B, Smith RA, Chen HH, Duffy SW. Quantifying the potential problem of overdiagnosis of ductal carcinoma in situ in breast cancer screening. Eur J Cancer 2003; 39:1746-1754

If a woman has dense breasts, what should be considered?

22. Does supplemental screening beyond mammography save lives?X

Mammography is the only imaging screening modality that has been studied by multiple randomized controlled trials. Across those trials, mammography has been shown to reduce deaths due to breast cancer. The randomized trials which show a benefit from mammography are those in which mammography increased detection of invasive breast cancers before they spread to lymph nodesi. No randomized controlled trial has ever been performed on any other imaging screening modality and therefore there are no data showing that supplemental screening will or will not decrease mortality though it is expected that other screening tests which increase detection of node-negative invasive breast cancers beyond mammography should further reduce breast cancer mortality.

Proving the mortality benefit of any supplemental screening modality would require a very large, very expensive randomized control trial with 15-20 years of follow-up. Given the speed of technological developments, any results would likely be obsolete by the trial's conclusion. We do know that high-risk women having annual MRI screening are less likely to have advanced breast cancer than their counterparts who were not screened with MRIii. We also know that average-risk women who are screened with ultrasound in addition to mammography are unlikely to have palpable cancer in the interval between screens iii,iv with the rates of such "interval cancers" similar to women with fatty breasts screened only with mammography. The cancers found only on MRI or ultrasound are mostly small invasive cancers (average size of about 1 cm) which are mostly node negative v,vi; MRI also finds some DCIS. These results suggest there is a benefit to finding additional cancers with supplemental screening, though it is certainly possible that, like mammography, some of the cancers found with supplemental screening are slow growing and may never cause a woman harm, even if left untreated.

iSmith RA, Duffy SW, Gabe R, Tabar L, Yen AM, Chen TH. The randomized trials of breast cancer screening: what have we learned? Radiol Clin North Am 2004; 42:793-806, v

iiWarner E, Hill K, Causer P, et al. Prospective study of breast cancer incidence in women with a BRCA1 or BRCA2 mutation under surveillance with and without magnetic resonance imaging. J Clin Oncol 2011; 29:1664-1669

iiiCorsetti V, Houssami N, Ghirardi M, et al. Evidence of the effect of adjunct ultrasound screening in women with mammography-negative dense breasts: interval breast cancers at 1 year follow-up. Eur J Cancer 2011; 47:1021-1026

ivBerg WA, Zhang Z, Lehrer D, et al. Detection of breast cancer with addition of annual screening ultrasound or a single screening MRI to mammography in women with elevated breast cancer risk. JAMA 2012; 307:1394-1404

vBerg WA. Tailored supplemental screening for breast cancer: what now and what next? AJR Am J Roentgenol 2009; 192:390-399

viBrem RF, Lenihan MJ, Lieberman J, Torrente J. Screening breast ultrasound: past, present, and future. AJR American journal of roentgenology 2015; 204:234-240

23. If my dense-breasted patient would like to consider supplemental screening, how should I write the order?X

As this may depend on each practice and what technology is available, and as the initial mammogram may vary (2D mammogram, 2D+3D mammogram or 3D+synthetic mammogram) by practice, it can be useful to ask your local radiology facility for direction on writing the order.

Mammography using3D/tomosynthesis is the preferred primary screening modality. If a patient is at high risk for breast cancer, supplemental screening with MRI is also appropriate (if she can tolerate that). If a woman has dense breasts and, after discussion, she desires supplemental screening ultrasound, an order can be written as follows:

  • "Digital breast tomosynthesis/3D mammogram if available; if mammographically dense tissue, then perform screening ultrasound."

It may be possible to create a conditional, contingent order with the imaging facility or Radiology Department; indicating “additional testing permitted;” and/or to work with administration to add supplemental imaging to the electronic ordering system. While supplemental dense breast screening with MRI detects more cancers than ultrasound, such MRI may not be covered by insurance and is more often reserved for those women who are at high risk.

24. Should a routine annual mammogram for a woman with dense breasts be scheduled as a "diagnostic" or a "screening" mammogram?X

Screening. "Diagnostic" mammography is monitored by the radiologist during the appointment and "screening" mammography is not. Indications for diagnostic mammography, rather than screening, include signs and symptoms of breast cancer such as a lump, bloody or spontaneous clear nipple discharge, skin or nipple retraction. If additional targeted imaging or follow-up is needed for an abnormality seen on the most recent prior breast imaging, a "diagnostic" appointment is also appropriate. In diagnostic breast imaging, additional views or ultrasound may be performed at the same visit if they are needed. The radiologist will interpret the breast imaging during the examination and the woman will leave with her results after a diagnostic mammogram. Women with a personal history of breast cancer can have their routine annual mammograms performed as diagnostic or screening examinations at many facilities. Diagnostic mammography is typically covered by insurance but subject to deductible and copay.

"Screening" mammography is fully covered by insurance under the Affordable Care Act for women over the age of 40 in the United States and may be covered for younger women, if recommended by her physician, depending on the insurance policy. Typically, screening mammograms are interpreted in a quiet, uninterrupted environment with the full benefit of prior examinations. Cancers are better detected and fewer unnecessary additional views (with associated radiation exposure) are recommended in the screening setting. Results are usually sent by mail to the patient within a few days to a week (by law not later than 30 days) after the appointment.

25. If a patient has dense breasts, what additional screening tests are available after a mammogram?X

Depending on the patient's age, risk level (for further explanation see section on "Risk Assessment Tools") and breast density, additional screening tools, such as ultrasound or MRI, may be recommended in addition to mammography. The addition of another imaging tool after a mammogram will find more cancers than mammography/tomosynthesis alone

It is important to reassure the patient that it is normal for any screening test to find things that may need to be looked at more closely by additional testing. While some of these additional findings may be cancerous, the vast majority will not (this is known as a "false positive"); the only way to determine the importance of such findings is through additional imaging and sometimes biopsy.

Both 2D and 3D mammograms are x-ray technologies. X-rays have difficulty penetrating dense tissue and, as such, are more effective in fatty breasts than in extremely dense breasts. Early results suggest that ultrasound finds additional cancers hidden by dense tissue even after 3D mammography, though further study is warranted.

2D and 3D mammogram cancer find (detection) rates

If 1,000 Women Are Screened With

Number of Women Found to Have Cancer

Type of Technology

Regular 2D-mammogram alone


Ionizing Radiation (x-rays)

Tomosynthesis (“3D” mammography)


Ionizing Radiation (x-rays)

* Mammography performance in dense breasts is slightly improved when digital, rather than film, technique is used, though the ranges stated apply to either.

Ultrasound: Ultrasound is the only screening test suggested specifically for women with dense breasts as a supplement to mammography. In dense tissue, physician-performed ultrasound has been shown to find another 3-4 cancers per 1000 women screened that were not seen on mammography. Technologist-performed ultrasound or automated whole breast ultrasound using special equipment results in detection of another 2-3 cancers per 1000 women screened. Like all screening tools, ultrasound also detects many findings that are not cancer, but that may require follow-up imaging and/or biopsy. There is no x-ray radiation from ultrasound.

MRI: Contrast-enhanced magnetic resonance imaging (MRI) can find the most breast cancers of any imaging test currently in widespread use. A woman at very high risk for breast cancer (due to a known or suspected mutation in a breast cancer causing gene, or due to a greater than 20% lifetime risk for breast cancer according to the Claus, Tyrer-Cuzick, or other model that predicts risk for pathogenic BRCA mutationi) may be eligible to begin screening at age 25 or at least by age 30. In high-risk women, MRI is recommended annually in addition to mammography regardless of breast density, though before age 30 sometimes only MRI is performed due to the radiation sensitivity of younger breast tissue. Annual screening MRI is also recommended in women who have had prior radiation therapy to the chest at least 8 years earlier and before age 30, such as for Hodgkin's lymphoma. Recently, the American College of Radiology recommended annual screening MRI also in women with a personal history of breast cancer diagnosed by age 50 and in women diagnosed later who have dense breasts.ii Annual supplemental screening MRI can also be considered in women who have a personal history of atypical or risk lesions such as lobular carcinoma in situ.

MRI of the breasts requires intravenous injection of gadolinium-based contrast and lying in a tunnel-like space that may be difficult for women with claustrophobia. There is no x-ray radiation from MRI. Gadolinium has been shown to accumulate in parts of the brain but no adverse effects have been shown from this.

MRI's have many false positives (when additional testing or biopsy is recommended for a finding which is not cancer). The benefits and risks of MRI in women who are not at high risk are being studied. In most centers, MRI is a very expensive imaging test that is not covered by insurance unless a woman meets high-risk definitions, and a copay and/or deductible may be incurred. MRI cannot be performed in women with poor kidney function, pacemakers, or certain other metal implants.

i Saslow, D, Boetes, C, Burke, W, et al. (2007). American Cancer Society Guidelines for Breast Screening with MRI as an Adjunct to Mammography. CA: A Cancer Journal for Clinicians, 57: 75–89. This article is available online at CA Online

iiMonticciolo DL et al. J Am Coll Radiol. 2018 Mar;15(3 Pt A):408-414. doi: 10.1016/j.jacr.2017.11.034. Epub 2018 Jan 19

The addition of screening ultrasound is usually only recommended in women with dense breasts. Screening MRI is used in high-risk women of all breast densities. If screening MRI is performed, there is no need for screening ultrasound.

Table 2. Summary of Cancer Detection and Recall Rates for Commonly Available Breast Screening Tests

If 1,000 Women Are Screened With

Number of Women Found to Have Cancer

Type of Technology

Number of Women Called Back for More Testing

Regular 2D-mammogram alone


Ionizing Radiation


Tomosynthesis (“3D” mammography)


Ionizing Radiation


Regular 2D-mammogram plus ultrasound (US) *


Ionizing Radiation plus Sound waves


Regular 2D-mammogram plus contrast-enhanced MRI


Ionizing Radiation plus Magnetic field and intravenous contrast


Courtesy of Dr. Wendie Berg

* One prospective multicenter trial in Italy (ASTOUND) examined ultrasound and 3D mammography after 2D mammography, reporting ultrasound identified 7 more cancers per 1000 women screened compared to 4 more cancers per 1000 women screened with 3D mammography.

Note: On average, out of 1000 women screened with mammography, 100 will be recalled for additional testing. Of those 100 women recalled: 60 will be found to have nothing of concern; 20 will be recommended for short interval follow-up of a "probably benign" finding (specific type of mass or calcifications with < 2% risk of malignancy, for which follow-up is a safe alternative to immediate biopsy); and 20 will be recommended for biopsy, of whom 5 on average will be found to have cancer.iii

MBI, BSGI and contrast-enhanced Mammography may be offered at some centers though further validation is needed.

iii Rosenberg, RD, Yankaskas, BC, Abraham, LA, et al. (2006). Performance benchmarks for screening mammography. Radiology 241(1)

26. Will insurance cover supplemental screening beyond mammography?X

In the U.S., the answer depends on the type of screening, patient's insurance, risk factors, the state you practice in, and whether or not a law is in effect requiring insurance coverage for additional screening. In Illinois, for example, if ordered by a physician, a woman with dense breasts can receive an ultrasound without a copay or deductible. In New York as of January 1, 2017 all supplemental screening and diagnostic breast imaging are required to be fully covered (no copay/no deductible), though exceptions do exist. In Connecticut, an ultrasound co-pay for screening dense breasts cannot exceed $20. Generally, in other states, an ultrasound will be covered if ordered by a physician - but is subject to the copay and deductible of an individual health plan. In New Jersey, insurance coverage is provided for additional testing if a woman has extremely dense breasts. An MRI will generally be covered if the patient meets "high-risk" criteria*. In Michigan, at least one insurance company will cover a screening MRI for normal-risk women with dense breasts at a cost which matches the copay and deductible of a screening mammogram (which in most cases is zero). It is important for the patient to check with her insurance carrier prior to having an MRI.

In Europe, national breast screening programs for women of average risk are offered free in nearly all European countries adhering to standards laid out in the European Guidelines for Quality Assurance in Breast Cancer Screening and Diagnosis. Variations do exist on the ages and risk factors of women invited to participate in routine screening, screening intervals, coverage and supplemental screening modalities utilized. Opportunistic mammography exists in some countries either as the sole screening system or in addition to the national breast screening program. Part of the cost is out of pocket payment or reimbursed by private insurance.

*For more information on high-risk criteria, see American Cancer Society guidelines: http://www.cancer.org/cancer/breastcancer/moreinformation/breastcancerearlydetection/breast-cancer-early-detection-acs-recs

27. Does 3D mammography (tomosynthesis) solve the problem of screening dense breasts? X

Compared to standard digital mammography, 3D mammography (tomosynthesis) does improve the chance of finding cancer in most breasts, though cancer detection may not be improved in extremely dense breasts. This is because dense tissue can still hide cancers on tomosynthesis. 3D does reduce the chance of having to return for additional diagnostic imaging for a false positive finding (false alarm). Results from a prospective multicenter study in Italy (ASTOUNDi) showed that adding ultrasound significantly improved detection of cancer even after the combination of 2D and 3D mammography in dense breasts.

i(2016). Taglifico AS, Calabrese M. Mariscotti G, et al. Adjunct screening with tomosynthesis or ultrasound in mammography-negative dense breasts (ASTOUND): Interim report of a prospective comparative trial. J Clin Onco. Epub March 9, 2016

28. If a 3D mammo (tomo) is performed, will a patient also need a screening ultrasound or MRI?X

If a patient has dense breasts, and depending on her overall breast cancer risk, the answer is yes. In the ASTOUNDi prospective multicenter trial in Italy, ultrasound significantly improved detection of cancer even after tomosynthesis (3D mammography) in women with dense breasts. If a patient has been recommended to have MRI screening, she would still have MRI even if tomosynthesis is performed. But if she has MRI screening, she doesn’t need screening ultrasound.

i(2016). Taglifico AS, Calabrese M. Mariscotti G, et al. Adjunct screening with tomosynthesis or ultrasound in mammography-negative dense breasts (ASTOUND): Interim report of a prospective comparative trlal. J Clin Onco. Epub March 9, 2016

29. If recommended to have additional screening with ultrasound or MRI, will a patient need to have that every year?X

Usually the answer is yes, though age and other medical conditions will change a patient's personal risk and benefit considerations and therefore screening recommendations may change from one year to the next. Technology is changing and guidelines also evolve which influence recommendations.

30. Is gadolinium contrast used in MRI imaging safe?X

Gadolinium, a heavy metal, is injected intravenously as a contrast agent to help see breast cancer on MRI examinations. Most of the gadolinium is cleared by the kidneys. There are data showing that small amounts of gadolinium can accumulate in parts of the brain, especially after multiple MRI examinations. The importance of this finding is unknown and has not been linked to any known negative health effects in patients with normal kidney function. There appears to be more gadolinium kept in the body with certain types of contrast agents (so-called "linear" compounds) than with those that are more like a cage around the gadolinium (so-called "macrocyclic" compounds). When kidney function is less than normal, the dose of contrast used may be reduced. Gadolinium contrast should not be used in a patient who is pregnant or who may be pregnant. The Food and Drug Administration has concluded that the benefit of all approved gadolinium-based contrast agents far outweighs any hypothetical risks. Experts on our Medical Advisory Board agree, and we continue to recommend annual contrast-enhanced MRI for women at high risk. For further information, please see: https://www.fda.gov/Drugs/DrugSafety/ucm589213.htm.

31. Is MBI or BSGI recommended for screening dense breasts?X

Molecular Breast Imaging (MBI) is a specialized nuclear medicine breast imaging technique that requires intravenous injection of a radiopharmaceutical, typically 99mTc-sestamibi. Sestamibi has been in common use as a tracer for nuclear cardiology studies for over 30 years and has an extremely low risk of adverse reactions and no contraindications. Low-dose molecular breast imaging has been used with excellent results by The Mayo Clinic and a few other centers for screening women with dense breasts, showing another 7 to 8 cancers after a normal mammogram for every thousand women screened.i,ii,iii

Breast Specific Gamma Imaging (BSGI) is also a nuclear medicine breast imaging technique that requires intravenous injection of a radioactive agent. Due to differences in equipment, it requires a higher radiation dose than MBI and is not recommended for routine screening.

MBI or BSGI can be useful diagnostic tools in women who have dense breasts and symptoms such as a lump or vague abnormality on mammography that rarely cannot be otherwise sorted out with additional views or ultrasound. MBI or BSGI can also be helpful for some women who need but cannot have an MRI. As of the most recent review in 2017, the American College of Radiology Practice Parameter for Molecular Breast Imagingiv suggests MBI is a potential option for supplemental screening in high-risk women and those with dense breasts who cannot undergo MRI, but it is usually not indicated as the technique involves ionizing radiation to the whole body with attendant risk of potentially inducing cancer.v These tests are never used in women who are pregnant.

The radiation exposure from low-dose MBI, performed with a delivered dose of 6 to 8 mCi 99mTc-sestamibi, is higher than that from a mammogram. Further, mammography delivers radiation to the breast only, while MBI and BSGI deliver radiation to the whole body. In order to compare radiation doses from these different types of exams, a standard calculation called "effective radiation dose" is used, which takes into account which body parts are exposed to radiation by a given test and how sensitive every exposed organ is to radiation. Effective dose has units of milli-Sieverts (mSv). The effective dose of mammography is about 0.5 mSv and the effective dose from a low-dose MBI is about 1.8 to 2.4 mSv. BSGI has a higher effective dose of between 4.5 and 9 mSv. For comparison, the radiation dose received from normal daily life is between 2 and 10 mSv per year, depending on where you live. Below effective doses of 50 mSv, health risks from radiation are "too low to be detectable and may be nonexistent", according to national and international radiation physics experts.vi,vii

Chart 1.Graph compares the effective radiation dose (mSv) to the whole body from common medical exams (CT = computed tomography; PET = positron emission tomography). Annual background radiation is between 2 and 10 mSv (greater at higher elevations such as Denver, CO). The annual limit for radiation workers is 50 mSv, below which it is considered unlikely to observe cancers caused by radiation exposure. Any risk from radiation is greater in younger individuals, especially those under the age of 30, and radiation exposure should always be minimized (except when undergoing treatment of a known cancer).

iRhodes, DJ, Hruska, CB, Philips, SW, et al. Dedicated dual-head gamma imaging for breast cancer screening in women with mammographically dense breasts. Radiology 2011; 258:106-118.

iiRhodes DJ, Hruska CB, Conners AL, et al. JOURNAL CLUB: Molecular Breast Imaging at Reduced Radiation Dose for Supplemental Screening in Mammographically Dense Breasts. AJR American Journal of Roentgenology 2015; 204:241-251.

iiiShermis RB, Wilson KD, Doyle MT, et al. Supplemental Breast Cancer Screening With Molecular Breast Imaging for Women With Dense Breast Tissue. AJR Am J Roentgenol 2016:1-8



viHealth Physics Society statement: https://hps.org/documents/radiationrisk.pdf ; American Association of Physicists in Medicine statement:http://www.aapm.org/org/policies/details.asp?id=318&type=PP&current=true

viiUnited Nations Scientific Committee on the Effects of Atomic Radiation. In: United Nations, ed. Biological mechanisms of radiation actions at low doses. New York, NY: United Nations 2012

32. Should thermography be used to screen dense breasts?X

No. According to the FDA, "Despite widely publicized claims to the contrary, thermography should not be used in place of mammography for breast cancer screening or diagnosis."i

Thermography is a non-invasive technique that uses infrared technology to detect both heat and blood flow patterns very near the skin's surface. Although some large cancers can be seen, these are usually palpable and so thermography adds little. Thermography has a high "false negative" rate (when a test result indicates "no cancer" – though cancer is actually present), especially for small breast cancers, so it does not play a role in screening asymptomatic women. Thermography also has a high rate of “indeterminate” findings, which on additional diagnostic evaluation (mammography, ultrasound, MRI, follow-up observation, etc.) indicate no cancer is found. These often prompt a recommendation for short interval follow-up, which creates anxiety and adds to the cost to the woman.

i(2011). Thermogram no substitute for mammogram. U.S. Food and Drug Administration. Retrieved from http://www.fda.gov/forconsumers/consumerupdates/ucm257499.htm

33. Can the decision on supplemental screening this year be based on patient's breast density last year?X

The answer is essentially "yes". At the population level, there is a tendency for slight decrease in breast density each year, and this tends to be more abrupt in the few years around menopause. One studyi showed that only 7% of women who were considered not dense one year were classified as "dense" the following year; similarly 6% of women considered "dense" one year were classified as not dense the following year. For 87% of women, there was no change from one year to the next. Any difference that might affect the decision for supplemental screening would be between women considered to have heterogeneously dense or scattered fibroglandular density one year or the other, and radiologists may differ in this assessment even when there is no true change in the breasts. In a patient with breast density near the threshold, there are likely to be areas in the breast where cancer could be masked: it is not unreasonable to have had supplemental screening even if one's breasts turn out to be slightly less dense this year.

iCohen SL, Margolies LR, Schwager SJ, et al. Early discussion of breast density and supplemental breast cancer screening: is it possible? The breast journal 2014; 20:229-234

What Are Factors That May Affect Breast Density?

34. Can breast density be changed with diet? Is fat in the diet related to breast density? X

Dietary fat intake has little to do with breast density; however, it does relate to increased body mass index (BMI). BMI is a measure of body fat based on height and weight, and there is more fatty breast tissue in women with higher BMI. Higher BMI reduces the percent density but may not reduce the total amount of dense tissue. BMI and breast density are both separate risk factors for breast cancer. Before menopause, low BMIi,ii increases the risk of breast cancer. After menopause, weight gain and increasing BMI increase the risk of breast cancer.

iVan den Brandt, PA, Spiegelman, D, Yaun, SS, et al. (2000). Pooled analysis of prospective cohort studies on height, weight and breast cancer risk. American Journal of Epidemiology 152(6): 514-27.

iiHuo, CW, Chew, GL, Britt KL, et al. (2014). Mammographic density-a review on the current understanding of its association with breast cancer. Breast Cancer Res Treat 144(3):479-502

35. Does taking estrogen affect breast density?X

An increase in mammographic density is much more common among women taking continuous combined (estrogen plus progesterone) hormonal therapy (seen in 21-43% of such women) than for those using oral low-dose estrogen (6%) or transdermal (2%) estrogen treatment. The increase in density is often apparent at the first visit after starting hormonal therapy. Due to the increased risk of breast cancer in women taking combined hormonal therapy, recommendations are that use not extent beyond 3 to 5 years.i

Crandall, CJ, Aragaki, AK, Cauley, JA, et al. (2012). Breast tenderness after inititation of conjugated equine estrogens and mammographic density change. Breast Cancer Research and Treatment 131(3):969-979. Retrieved from http://www.ncbi.nlm.nih.gov/pubmed/21979747

Grady, D, Vittinghoff, E, Lin, F, et al. (2007). Effect of ultra-low-dose transdermal estradiol on breast density in postmenopausal women. Menopause 14(3 Pt 1):391-396. Retrieved from http://www.ncbi.nlm.nih.gov/pubmed/17224859

Nielsen, M, Raundahl, J, Pettersen, P, et al. (2009). Low-dose transdermal estradiol induces breast density and heterogeneity changes comparable to those of raloxifene. Menopause 16(4):785-791. Retrieved from http://www.ncbi.nlm.nih.gov/pubmed/19322115

Chlebowski RT, Anderson GL, Gass M, et al. Estrogen plus progestin and breast cancer incidence and mortality in postmenopausal women. JAMA 2010; 304:1684-1692

iMenopause.org (2018). The 2012 Hormone Therapy Position Statement of the North American Menopause Society. Available at : http://www.menopause.org/docs/default-document-library/psht12.pdf?sfvrsn=2 [Accessed 13 June 2018]

36. Is there anything a patient can do to decrease her breast density? What about taking tamoxifen?X

Tamoxifen blocks the estrogen receptor in breast cells and in breast cancer cells which express the estrogen receptor. Tamoxifen may be recommended to reduce the risk of developing breast cancer in women who have had prior atypical biopsies. Tamoxifen is also prescribed for women who have had breast cancer that expresses estrogen receptors to decrease recurrence. One studyi found that when breast density is carefully measured by computer software, women whose breasts became at least 10% less dense while taking the drug had a 63% reduction in risk of developing breast cancer - whereas those whose breast density did not change did not see a decrease in their risk. Several similar studiesii,iii,iv in women who have had breast cancer showed that only women whose breast density decreased on tamoxifen had decreased risk of recurrence. Tamoxifen also carries about a 3% risk of blood clots (which could result in pulmonary embolism or stroke) and a smaller risk of endometrial cancer (if the woman still has her uterus).

If a woman is on hormone therapy for menopausal symptoms, her breast density may decrease if she stops taking hormone supplements.

iCuzick, J. (2012). Breast density predicts endocrine treatment outcome in the adjuvant setting. Breast Cancer Research 2012 14 (109). Retrieved from http://breast-cancer-research.com/content/14/4/109

iiYee, KM. (2013). Changes in breast density point to tamoxifen's effectiveness. Auntminnie.com. Retrieved from http://www.auntminnie.com/default.aspx?sec=ser&sub=def&pag=dis&ItemID=103197

iiiCuzick, J, Warwick, J, Pinney, E, et al. (2011). Tamoxifen-induced reduction in mammographic density and breast cancer risk reduction: A nested case-control study. Journal of the National Cancer Institute 103(9): 744-752. Retrieved from http://www.ncbi.nlm.nih.gov/pubmed/21483019

ivLi, J, Humphreys, K, Eriksson, L, et al. (2013). Mammographic density is a prognostic marker of response to adjuvant tamoxifen therapy in postmenopausal patients with breast cancer. Journal of Clinical Oncology (31): 2249-2256. Retrieved from http://jco.ascopubs.org/content/early/2013/04/22/JCO.2012.44.5015.abstract

37. Will taking Arimidex or other aromatase inhibitors affect breast density?X

Aromatase inhibitors block the body's own production of estrogen and are prescribed for postmenopausal women who have had breast cancer where the tumor cells express receptors for estrogen. One studyi looked at women who have had breast cancer. When breast density is carefully measured by computer software, women who experienced a decrease in breast density while taking tamoxifen or aromatase inhibitors had a lower risk of recurrence than women who did not experience a decrease in breast density.

iKim, J, Han, W, Moon, H, et al. (2012). Breast density change as a predictive surrogate for response to adjuvant endocrine therapy in hormone receptor positive breast cancer. Breast Cancer Research 2012 14(403). Retrieved from http://breast-cancer-research.com/content/14/4/R102

Kim, J, Han, W, Moon, H, et al. (2012). Correction: Breast density change as a predictive surrogate for response to adjuvant endocrine therapy in hormone receptor positive breast cancer. Breast Cancer Research 2012 14(403). Retrieved from http://breast-cancer-research.com/content/14/6/403

38. For breast cancer survivors, is there a correlation between dense breasts and the likelihood of cancer in the opposite breast?X

Yes. There is a 1.8-fold higher risk of cancer in the opposite breast among women with dense breastsi, but density and associated risk can be reduced with treatment. A 10% decrease of mammographic density or more within the first two years after an original diagnosis, as a result of treatment, is associated with a significantly reduced risk of cancer in the opposite breast (known as contralateral breast cancer)ii. This potential new risk predictor can thus contribute to decision-making in follow-up treatment - particularly the continuation of a chemoprevention drug, like tamoxifen or aromatase inhibitors, which reduce breast density in some womeniii.

iRaghavendra A, Sinha AK, Le-Petross HT, et al. (2017). Mammographic breast density is associated with the development of contralateral breast cancer. Cancer. 123(11):1935-194

iiSandberg, M, Li, J, Hall, P, et al. (2013). Change of mammographic density predicts the risk of contralateral breast cancer – a case control study. Breast Cancer Research (15). Retrieved from http://breast-cancer-research.com/content/15/4/R57

iiiEngmann NJ, Scott CG, Jensen MR, et al. (2017). Longitudinal Changes in Volumetric Breast Density with Tamoxifen and Aromatase Inhibitors. Cancer Epidemiol Biomarkers Prev. 26(6):930-937

39. Is breast density an issue which affects men?X

Not normally, though rarely men do get breast cancer. Normal male breasts are mostly fatty. Sometimes men's breasts do become enlarged and develop glandular tissue due to a condition called gynecomastia. This enlargement, due to a hormonal imbalance, normally affects one breast more than the other. If a mammogram is performed, it is usually easy to distinguish gynecomastia from breast cancer.

40. Does exercise affect breast density?X

No. However exercise can decrease the amount of fat in the breast and as “breast density” reflects the relative amount of fibroglandular (dense) tissue and fat, the apparent density may increase.

41. Is breast density inherited?X

Breast density is at least partially inherited, though it is complex to predict. If a patient's mother had dense breast tissue, it's more likely she will, too.

42. Does the increase in density due to breastfeeding affect the ability of screening tests, like a mammogram, to find breast cancer?X

Yes. Changes in the breast during breastfeeding do reduce the accuracy of screening tests (like mammography or MRI). Unless the patient plans to be breastfeeding for more than one to two years and is at high risk, it is generally recommended to wait at least a few months after breastfeeding stops before resuming breast screening. Ultrasound is usually performed first if a patient is breastfeeding and there is a concern about breast symptoms. If a breastfeeding woman needs to undergo breast imaging, it is advisable to nurse or pump immediately before the exam.

43. Do African-American women have denser breasts?X

There have been conflicting studies on whether African-American women have denser breasts than women of other races. One studyi indicated they do not, while a more recent studyii indicated they do.

iReference: Del Carmen, MG, Halpern, EF, Kopans, DB, et al. (2007). Mammographic breast density and race. American Journal of Roentgenology 138(4): 1447-1150. Retrieved from http://www.ncbi.nlm.nih.gov/m/pubmed/17377060/

iiMcCarthy AM, Keller BM, Pantalone LM, et al. (2016). Racial Differences in Quantitative Measures of Area and Volumetric Breast Density. J Natl Cancer Inst 108

44. Are there any special considerations for screening of African-American or Hispanic women?X

African-American women are more likely to have disease-causing mutations in BRCA and the American College of Radiology recommends they be evaluated in a high-risk program by age 30, even in the absence of family history.i Further, it is more important for African-American women and Hispanic women to start screening at least by age 40 as peak breast cancer incidence occurs in the mid 40s, compared to peak in the early 50s for Caucasian women.ii

iMonticciolo DL, Newell MS, Moy L, Niell B, Monsees B, Sickles EA. (2018). Breast Cancer Screening in Women at Higher-Than-Average Risk: Recommendations From the ACR. J Am Coll Radiol15:408-414

iiStapleton SM, Oseni TO, Bababekov YJ, Hung YC, Chang DC. (2018). Race/Ethnicity and Age Distribution of Breast Cancer Diagnosis in the United States. JAMA SurgJun 1;153(6):594-595

45. Do Asian women have denser breasts?X

Generally, Asian women do have denser breasts than women of other races.

46. Is there a relationship between having dense breasts and pathogenic BRCA gene mutations?X

Disease-causing BRCA gene mutations and dense breasts are each independent risk factors for the development of breast cancer; however, pathogenic BRCA1 or BRCA2 mutations are associated with a much higher risk than that of having dense breasts. As BRCA1 and BRCA2 mutations are associated with a higher risk, MRI is part of routine screening beginning at age 25 to 30 for women who have these mutations, regardless of breast density. Cancers are also more likely to develop at a younger age in women with disease-causing mutations in BRCA genes, and the breasts are usually dense at younger ages making mammography especially ineffective as a standalone test in such women.

47. How do women under the age of 40 find information about breast density and their risks for breast cancer?X

Dense breasts are mostly an issue affecting mammography performance so that a patient generally does not need to know until they begin having mammograms. For women at normal risk, mammography is often recommended to begin at age 40. If a woman has a family history of breast cancer and has not begun mammography screening, she should speak to her doctor about personal risk factors English | Spanish and when mammography and possibly other screening should begin. As a general guide, if a woman’s mother or sister had breast cancer diagnosed before age 50, she may want to begin annual screening 10 years before the relative’s age at diagnosis, but not before age 30.

European guidelines recommend double-read biennial screening digital mammography for average-risk women 50 to 69 years of age. Also encouraged are biennial screening for women 73 to 75 years of age, and annual screening for ages 40–45 to 49.i

iSardanelli F, Aase HS, Alvarez M, et al. (2017). Position paper on screening for breast cancer by the EUSOB and 30 national breast radiology bodies. European Radiology, July;27(7): 2737–2743.

A version of this material titled Breast Density: Are You Informed? was originally published in Imaging Technology News, April 2014.

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