A study published in Annals of Internal Medicine using mathematical modeling suggests looking at the level of risk for breast cancer for women in their 40s would aid in determining which women would benefit from mammography screening. In this study, investigators from the NCI’s Cancer Intervention and Surveillance Modeling Network (CISNET) used simulation models to determine the threshold of risk needed for women ages 40–49 to have comparable benefits and harms as when average-risk women aged 50–74 are screened every other year using mammography. The model estimated harm as the number of false positives but did not include the possibility of overdiagnosis.

The researchers found that the benefits and harms from screening mammograms every two years for women ages 40-49 are similar to those for average-risk women ages 50-74 when the younger women have a twofold increased risk of breast cancer. Women in their 40s must have a fourfold increased risk of breast cancer for the benefits and harms of annual screening to be similar as for 50 to 74-year-olds of average risk. The models found only small differences in benefits between film and digital mammography, with digital having many more false-positive results than film.

An accompanying meta-analysis and new analysis of Breast Cancer Surveillance Consortium data determined which factors increased risk of breast cancer for women in their 40s, and defined the magnitude of risk associated with each. Nelson and colleagues found that having a first-degree relative with breast cancer (especially one under age 50) and having extremely dense breasts on a mammogram increased risk by more than twofold. It is important to note that the modeling study did not provide estimates for women with specific risk factors, but instead for women with specific risk levels. The harms and difficulties associated with evaluating mammograms in women with extremely dense breasts were not taken into account in the modeling study. Dr. Otis Brawley, president of the American Cancer Society, weighs in on these two studies in an editorial.

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