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Take Home Points

  • Starting April 1, 2013, California law requires that patients be informed if they have "dense breast tissue" on screening mammography, and if so, that they may want to discuss their "screening options" with their primary physician.


  • Approximately 50% of women undergoing screening mammography are classified as having either "heterogeneously dense" or "extremely dense" breasts. For all of these women, the patient letter will inform them that they have "dense breast tissue."


  • Only 10% of all women have "extremely dense" breast tissue, which is associated with a relative risk of breast cancer of approximately 2 compared with average breast density. 40% of women have "heterogeneously dense" breast tissue, which is associated with a relative risk of approximately 1.2. Therefore, breast density is not a major cancer risk factor.


  • The sensitivity of mammography is reduced as background breast tissue density increases. When mammography is the only screening test performed, sensitivity decreases by 10% to 20% for women with "dense breasts".


  • The recommendations for screening mammography are exactly the same for women with dense breasts as for the rest of the population. Mammography is the only screening modality that has undergone randomized controlled trials demonstrating a reduction in breast cancer mortality. There is no recommendation that it be replaced with another test in any subset of the population.


  • For patients who are interested in additional screening options, a breast cancer risk assessment may be appropriate. It is a good starting point in the discussion of whether supplemental tests will be beneficial and what tests, if any, to order.


  • The other breast imaging "screening options" include screening MRI, ultrasound and tomosynthesis ("3D mammography"). Screening breast MRI has been shown to substantially increase the rate of cancer detection. It is recommended in patients who are at very high risk (>20% lifetime risk) based on American Cancer Society guidelines. For patients at "intermediate risk," such as those with a personal history of breast cancer or a prior biopsy diagnosis of atypia (equivalent to a 15% to 20% lifetime risk), a patient-centered shared decision-making approach is recommended.


  • Screening breast ultrasound is not offered at many centers and may entail an out of pocket charge to patients. Small studies have shown a modest increase in cancer detection, but also a high rate of false positives resulting in benign biopsies. The choice to have this test should be made on an individual basis after a discussion of these risks, benefits, and costs.


  • Breast tomosynthesis ("3D mammography") is being offered in addition to screening mammography in some centers. Thus far, we have preliminary encouraging data on the performance of tomosynthesis in women with dense tissue.