Not all women with dense breasts have high interval cancer rates, and therefore, breast density should not be used as the sole determinant for supplemental imaging. That is the key finding from a cohort study of 365,426 women ages 40 to 74 years old.

Investigators used Breast Imaging Reporting and Data System (BI-RADS) breast density ratings, Breast Cancer Surveillance Consortium (BCSC) 5-year breast cancer risk, and interval cancer rate (invasive cancer less than 12 months following a normal mammogram) per 1,000 mammography examinations, and found:

• High-interval cancer rates in women with a 5-year risk of 1.67% or greater and extremely dense breasts, and a 5-year risk of 2.5% and heterogeneously dense breasts.

• Interval rates of advanced-stage disease were highest in women with a 2.5% or greater 5-year risk and heterogeneously or extremely dense breasts.

• 5-year risk was low to average in 51% of women with heterogeneously dense breasts and 52.5% for those with extremely dense breasts.

The study authors suggest combining BI-RADS and BCSC 5-year risks to identify women at high risk for interval cancer.

Citation: Kerlikowske K, Zhu W, Tosteson AN, et al; Breast Cancer Surveillance Consortium. Identifying women with dense breasts at high risk for interval cancer: a cohort study. Ann Intern Med. 2015;162(10):673-681. doi:10.7326/M14-1465.

Commentary: Increased breast density decreases the sensitivity of mammography and is an established risk factor for breast cancer.¹ There is an increased risk of developing breast cancer for high compared to low breast density (odds ratio [OR], 3.5), and for developing a breast cancer in the 12 month interval between mammograms (OR, 17.8). In one study, 50% of cancers detected after a negative mammogram were attributable to breast density.² Breast density is routinely reported as part of the BI-RADS reporting system, and 21 states have legislation requiring direct reporting of breast density to patients. The role of ultrasound as an adjuvant screening modality in women with dense breasts is unclear. This study adds to the existent evidence showing that the risk of an interval breast cancer being detected is best viewed not as solely related to breast density but rather as a product of both 5-year risk, which can be calculated using the GAIL model,³ along with breast density. — Neil Skolnik, MD

1. Vachon CM, van Gils CH, Sellers TA, et al. Mammographic density, breast cancer risk and risk prediction. Breast Cancer Res. 2007;9(6):217. doi:10.1186/bcr1829.

2. Boyd NF, Guo H, Martin LJ, et al. Mammographic density and the risk and detection of breast cancer. N Engl J Med. 2007;356(3):227-236.

3. National Cancer Institute’s Breast Cancer Risk Assessment Tool