HEALTH CARE PROVIDERS FAQs
A version of this material titled Breast Density: Are You Informed? was originally published in Imaging Technology News, April 2014.
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 become less so 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. Fatty breasts can feel lumpy as the ligaments which 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 .
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. Information about breast density is usually included in a report sent from radiologist to referring doctor after a mammogram. Breast density information may also be included in the patient letter sent after their mammogram (depending on state law – see "Legislation" tab for more information).
A woman's breast tissue is categorized as one of four categories:
Courtesy of Dr. Wendie Berg
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.
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 is harder or 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), it usually can be seen easily, even when it is small. Because dense tissue can hide cancers, the fattier breasts are, the more effective the mammogram. As density increases, the ability of mammography to show cancers decreases. The images below are examples of how cancer displays 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 tissue. C) In this heterogeneously dense breast, a 4 cm cancer (arrows) is hidden by the dense breast tissue. Note metastatic node 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. Dense breasts are 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
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 tissue than for fatty tissue. Supplemental screening in addition to mammography should be considered for women with dense breasts.
Most women have breast density somewhere in the middle range, with risk 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. There is currently no reliable way to fully know the interplay of breast density, family history, prior biopsy results, and other . 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
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 hormonal 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. Cancer is more often found as a lump, i.e. more likely to be clinically detected in the interval between screens (i.e. "interval cancer," see Table 1), in women with dense breasts. Such interval cancers tend to be more aggressive with worse outcomes. Dense breasts also increase the risk of recurrence (if patient has not had radiation). Additionally cancers found in dense breasts are more often stage IIb and III, are more often multifocal or multicentric, and a mastectomy is more often needed.*
*Arora 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 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)
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 breasts*
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. 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.
* Kerlikowske 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
* Sprague 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.
Courtesy of Dr. Wendie Berg
11. If a woman does not have dense breasts, what should she do?X
Annual mammography is recommended if she is over the age of 40 and in good health. Tomosynthesis can be used in addition to mammography (or, in some centers, instead of mammography). 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 study* 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.** 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.***
* 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
** 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
** 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
*** 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." Dense breast tissue can hide cancer on a mammogram and can reduce the effectiveness of mammography screening. A "normal," "negative," or "benign" mammogram does not reliably exclude cancer in women with dense breasts. Women with dense breasts may have cancer detected soon after a "normal," "negative," or "benign" mammogram. This is known as an "interval cancer." Additional screening should be considered. See flow chart: Who Needs More Screening?
14. A patient recently had a "normal" mammogram and has extremely dense breasts. She now feels a lump. What should you recommend?X
A. It is important not to ignore a lump just because the recent mammogram was normal, especially if the breasts are dense. While cysts 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 direct 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 of 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 74i. Based on these results, the American Cancer Society recommends that women age 40 and older should have a screening mammogram every year and should continue to do so as long as they are in good health. Because it takes at least 7-9 years to see any benefit from screening in terms of reduced deaths from breast cancerii, only women with life expectancy more than 10 years should be recommended to undergo screening (and this applies to any supplemental screening as well). Even the healthiest 85-year-old women have an average life expectancy of only 10 yearsiii: mammography after age 85 should usually be limited to diagnostic evaluation of women with symptoms. Women with disease-causing mutations in BRCA should begin screening earlier and American Cancer Society recommendations include annual MRI:iv BRCA-1 carriers should begin by age 25, and BRCA-2 carriers by age 30.
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 Tabar L, Yen MF, Vitak B, et al. (2003). Mammography service screening and mortality in breast cancer patients: 20-year follow-up before and after introduction of screening. The Lancet 361(9367):1405-10.
iii Walter LC, Covinsky KE. (2001). Cancer screening in elderly patients: A framework for individualized decision making. JAMA 285:2570–2556.
iv 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
16. Should women with dense breasts still have mammography screening?X
Yes. Mammography is the first step in screening for most women (except those who are pregnant or breastfeeding where ultrasound can be performed, but screening is usually deferred until several months after the patient is no longer pregnant or breastfeeding). 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, due to slightly improved cancer detection using digital mammography.* 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 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.
*Pisano 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 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. 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 2D mammogram captures images from two different angles (or views). Tomosynthesis (3-D) 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 your breast. A "3D" mammogram is usually 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 you have both 2D and 3D, your 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 some centers instead of the standard 2D mammogram. The total radiation dose from tomosynthesis with synthetic 2D images is essentially the same as from a standard 2D mammogram.
18. Is the mammography recall rate or the false positive 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 recalled for additional testing as are women with non-dense breasts.* Relatedly, 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.
* McCarthy, 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).
* Lehman, 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..
19. 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*. 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).
* 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
* 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
20. 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)*. 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).
* Yen 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?
21. 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 MRI [ii]. 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.
[i] Smith 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
[ii] Warner 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
[iii] Corsetti 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
[iv] Berg 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
[v] Berg WA. Tailored supplemental screening for breast cancer: what now and what next? AJR Am J Roentgenol 2009; 192:390-399
[vi] Brem RF, Lenihan MJ, Lieberman J, Torrente J. Screening breast ultrasound: past, present, and future. AJR American journal of roentgenology 2015; 204:234-240
22. Should a routine annual mammogram for a woman with dense breasts be scheduled as a "diagnostic" or a "screening" mammogram?X
A. 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.
23. If a patient has dense breasts, what additional screening tests are available after a 2D 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, like tomosynthesis, 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 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.
Tomosynthesis (3D mammography). With tomosynthesis, multiple "projection" images are taken of the breast using the same positioning and compression as for standard mammography (but the breast stays in compression longer, typically 4 to 7 seconds). Images of the breast are then reconstructed as 1-mm slices (so that for an average 4 to 5 cm thick breast, there will be 40 to 50 images to review from each projection, i.e. 160 to 200 images for the standard 4-view mammogram). Tomosynthesis is often performed in addition to a standard 2D-mammogram ("combination mode"). 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, her breasts will receive nearly twice the amount of radiation as from a standard mammogram though the combined dose is still within standard safety limits. In some centers, tomosynthesis can be processed by computers to create an image similar to a standard 2D mammogram (known as a "synthetic 2D mammogram") and therefore the radiation dose is the same as a standard mammogram. In some situations, such as a recall for additional imaging, only tomosynthesis images are performed, and this may become the norm as synthetic 2D mammograms improve and undergo more widespread clinical validation.
A 2D mammogram finds about 2-7 cancers for every 1,000 women who have a mammogram. Another 1-2 cancers will be found per 1,000 women when tomosynthesis is added to a standard mammogram. Tomosynthesis also makes it easier to recognize normal overlapping tissue and therefore reduces the chance of being called back for additional views or an ultrasound.
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
2D-Mammogram plus or including 3D-mammogram (tomosynthesis)
Mammogram 2-7 + Tomosynthesis 1-2** = 3-9 total
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.
** Cancer detection rate for regular 2D mammogram plus tomosynthesis. Cancer detection rates for synthetic 2D mammography with tomosynthesis are not fully known but are estimated to be comparable.
Ultrasound: Ultrasound is the only screening test suggested specifically for women with dense breasts. 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 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 which 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 mutation*) 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. MRI of the breasts requires intravenous injection of contrast and lying in a tunnel-like space that may be difficult for women with claustrophobia. There is no x-ray radiation from MRI.
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 which 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.
* 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
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
2D-mammogram plus 3D-mammogram (tomosynthesis)
Mammogram 2-7 + Tomosynthesis 1-2
= 3-9 total
Regular 2D-mammogram plus ultrasound (US) *
Mammogram 2-7 + Ultrasound 2-4
= 4-11 total
Regular 2D-mammogram plus contrast-enhanced MRI
Mammogram 2-7 +
MRI 10 or more
= 12-17 or more total
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. [Reference:Rosenberg, RD, Yankaskas, BC, Abraham, LA, et al. (2006). Performance benchmarks for screening mammography. Radiology 241(1)]
MBI, BSGI and contrast-enhanced Mammography may be offered at some centers though further validation is needed.
24. Will insurance cover supplemental screening beyond mammography?X
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 beginning 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. For more information about insurance coverage by state, visit the Legislation Tab’s interactive map or table.
*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
25. 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. For women with dense breasts, 3D does reduce the chance of having to return for additional imaging for a resulting false positive finding. Results from a prospective multicenter study in Italy (ASTOUND) showed that adding ultrasound significantly improved detection of cancer even after the combination of 2D and 3D mammography in dense breasts. Without question, high-risk women should still have MRI if they are able to tolerate it, even if they have tomosynthesis.
26. If a 3D mammo (tomo) is performed, will a patient also need a screening ultrasound or MRI?X
If a patient has been recommended to have a MRI screening, she would still have MRI even if tomosynthesis is performed. In the ASTOUND prospective multicenter trial in Italy, ultrasound significantly improved detection of cancer even after tomosynthesis (3D mammography) in women with dense breasts.
*(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 trail. J Clin Onco. Epub March 9, 2016
27. 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.
28. 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. The Mayo Clinic has been using low-dose molecular breast imaging for screening women with dense breasts with excellent results, showing another 7 to 8 cancers after a normal mammogram for every thousand women screened.*
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. These tests are never used in women who are pregnant. Due to the relatively small number of research studies performed as of the last review in 2012, the technology currently does not meet the American College of Radiology's Appropriateness Criteria for screening.**
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.***
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).
*Rhodes, 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.
*Rhodes 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.
*** Health 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¤t=true
***United 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
29. Should thermography be used to screen dense breasts?X
No. Thermography is a non-invasive technique that uses infrared technology to detect both heat and blood flow patterns very near the skin's surface and some large cancers can be seen this way. However, thermography has a high "false negative" rate (when a test result indicates "no cancer" – though cancer is actually present), especially for small breast cancers, and a high rate of indeterminate findings, when follow-ups are recommended for observation, but ultimately no cancer is found. 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." *
*(2011). Thermogram no substitute for mammogram. U.S. Food and Drug Administration. Retrieved from http://www.fda.gov/forconsumers/consumerupdates/ucm257499.htm
30. 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 study* 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.
* Cohen 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?
31. 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 BMI* increases the risk of breast cancer. After menopause, weight gain and increasing BMI increase the risk of breast cancer.
* Van 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.
* Huo, 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
32. 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. Risk of breast cancer also increases in women taking combined hormonal therapy.
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
33. 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 study* 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 studies** 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).
* Cuzick, 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
** Yee, 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
** Cuzick, 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
** Li, 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
34. 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 study* 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.
* Kim, 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
35. For breast cancer survivors, is there a correlation between dense breasts and the likelihood of cancer in the opposite breast?X
A recent study* showed that 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). 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 women.
Sandberg, 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
36. Is breast density an issue which affects men?X
Not normally, though 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 from breast cancer.
37. Does exercise affect breast density?X
No. Exercise can increase the amount of muscle behind the breasts, but the actual breast tissue is not affected by exercise. Weight loss due to exercise may make the breasts appear denser due to loss of fat (because the quantity of fat decreases while the quantity of dense tissue stays the same).
38. 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.
39. Does the increase in density due to breastfeeding affect the ability of screening tests, like a mammogram, to find cancer in breasts?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.
40. 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 study* indicated they do not, while a more recent study** indicated they do.
*Reference: 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/
**McCarthy AM, Keller B, Synnestvedt M, Conant E, Armstrong K, Kontos D. Racial differences in quantitative measures of area and volumetric breast density [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; 2015. Abstract nr 2770
41. Do Asian women have denser breasts?X
Generally, Asian women do have denser breasts than women of other races.
42. 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.
43. How do young 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 the patient has a family history of breast cancer and has not begun mammography screening, they should speak to their doctor about personal and when mammography and possibly other screening should begin.