1. From a prospective cohort study, the highest rates of cancer and advanced-stage disease after digital mammography were in those with heterogeneously or extremely dense breasts who also had a high 5-year risk score.
Evidence Rating Level: 2 (Good)
Study Rundown: Studies have suggested that supplemental imaging in women with dense breasts may increase detection of asymptomatic cancer, but the impact of breast density on cancer risk is not well understood. To determine how to effectively identify women who would benefit from this supplemental imaging, the authors analyzed a cohort of digital mammographies from women from the Breast Cancer Surveillance Consortium (BCSC). The highest BCSC 5-year risk score was in women with extremely or heterogeneously dense breasts. However, over half of women with heterogeneously and extremely dense breasts had low to average BCSC risk. The highest interval cancer rates were in women with extremely dense breasts and intermediate BCSC risk and those with heterogeneously dense breasts and high BCSC risk. Together these two groups represent only 24% of all women with dense breasts and 12% of women receiving mammography screening overall. Interval advanced-stage disease rate was highest in women with high or very high BCSC risk and extremely or heterogeneously dense breasts, which represents 21% of women with dense breasts. The major limitation of this study is that they did not assess the impact of supplemental imaging. Overall, increased breast density alone does not always lead to a substantial increase in cancer risk, and thus other risk factors should be included in identifying candidates for supplemental breast imaging.
In-Depth [prospective cohort]: This study used the BCSC cohort of 831,455 digital mammographies, where digital mammography screening for breast cancer had an overall sensitivity of 81-87%, lower in women with extremely dense breasts. From the cohort of 365,426 women, 2696 were diagnosed with invasive breast cancer and were more likely to be older, white, have a >1.67% (intermediate) BCSC 5-year risk and have heterogeneously or extremely dense breasts. Forty-seven percent of all women had dense breasts, and the overall interval cancer rate for heterogeneously dense and extremely dense breasts were 0.58 – 0.63 per 1000 mammograms and 0.72 – 0.89 per 1000 mammograms, respectively. In addition to the current policy of using supplemental imaging in women with heterogeneously or extremely dense breasts, 5 additional strategies were simulated in a model. Using various combinations of BCSC risk cut-offs, age groups, and breast density categories, the model showed that using BCSC risk and breast density together found many of interval cancers while allowing 51-76% fewer women to be screened with supplemental imaging as suggested by current policy.
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