What Do I Need to Know About Dense Breasts?
1. Are screening mammography outcomes different for dense breasts vs. fatty breasts?
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 . Increasing breast density also increases the risk of recurrence in women with a history of breast cancer (especially if no radiation therapy is given) [2-5].
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)|
|≥ 75%||17.8 (4.8 to 65.9)|
1. 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
2. Eriksson L, Czene K, Rosenberg L, Humphreys K, Hall P. Possible influence of mammographic density on local and locoregional recurrence of breast cancer. Breast Cancer Res 2013; 15:R56
3. Cil T, Fishell E, Hanna W, et al. Mammographic density and the risk of breast cancer recurrence after breast-conserving surgery. Cancer 2009; 115:5780-5787
4. Huang YS, Chen JL, Huang CS, et al. High mammographic breast density predicts locoregional recurrence after modified radical mastectomy for invasive breast cancer: A case-control study. Breast Cancer Res 2016; 18:120
5. Lowry KP, Braunstein LZ, Economopoulos KP, et al. Predictors of surveillance mammography outcomes in women with a personal history of breast cancer. Breast Cancer Res Treat 2018; 171:209-215
6. Boyd NF, Guo H, Martin LJ, et al. Mammographic density and the risk and detection of breast cancer. N Engl J Med 2007; 356:227-236
2. Is it unusual to have dense breasts?
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 [1, 2].
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.
1. 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
2. Sprague BL, Gangnon RE, Burt V, et al. Prevalence of mammographically dense breasts in the United States. J Natl Cancer Inst 2014; 106
3. Is breast size related to breast density?
Smaller breasts tend to be dense, and large breasts are more often relatively fatty, but there is wide variation at the individual level.
4. If a woman has dense breasts, will she always?
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 inter- and intraobserver variability .
1. Destounis S, Arieno A, Morgan R, Roberts C, Chan A. Qualitative versus quantitative mammographic breast density assessment: Applications for the US and abroad. Diagnostics (Basel) 2017; 7
5. If a woman does not have dense breasts, what should she do?
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.
6. Does having dense breasts increase the chance of dying from breast cancer?
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 [2, 3]. 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 .
1. Chiu SY, Duffy S, Yen AM, Tabar L, Smith RA, Chen HH. Effect of baseline breast density on breast cancer incidence, stage, mortality, and screening parameters: 25-year follow-up of a Swedish mammographic screening. Cancer Epidemiol Biomarkers Prev 2010; 19:1219-1228
2. Gierach GL, Ichikawa L, Kerlikowske K, et al. Relationship between mammographic density and breast cancer death in the breast cancer surveillance consortium. J Natl Cancer Inst 2012; 104:1218-1227
3. Masarwah A, Auvinen P, Sudah M, et al. Very low mammographic breast density predicts poorer outcome in patients with invasive breast cancer. European radiology 2015; 25
4. 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 2017; 140:41-49