In a new study published in Annals of Internal Medicine researchers have suggested that supplemental imaging may not be necessary for all women with dense breasts on mammography and that breast density should not be the sole criterion to guide decisions about supplemental breast cancer screening.
Researchers carried out a prospective cohort study using data from the Breast Cancer Surveillance Consortium (BCSC) wherein they examined breast cancer risk and Breast Imaging Reporting and Data System (BI-RADS) density categories and determined which combinations are associated with high rates of interval cancer.
The study’s main outcome measures were BI-RADS breast density, 5-year breast cancer risk according to the BCSC risk model, and an interval cancer rate per 1,000 mammography exams. Interval cancer rate was defined as invasive cancer 12 months or less after a normal mammogram, and higher interval cancer rate was defined as more than 1 case per 1,000 exams.
The study involved 365,426 women 40 to 74 years of age and 831,455 digital screening mammograms. A total of 2,696 women received a diagnosis of invasive breast cancer within 12 months of their screening mammogram. Such a diagnosis was more likely in older women, white women, women with heterogeneously or extremely dense breasts, those with a BCSC 5-year risk of 1.67 per cent or higher, and those with a family history of breast cancer.
Denser breasts were more common among younger women. The researchers found that interval cancer rates were high in women with a 5-year breast cancer risk of 1.67 per cent or more and extremely dense breasts and in women with a 5-year risk of 2.50 per cent or more and heterogeneously dense breasts.
Women with a 5-year risk of 2.50 per cent or greater and heterogeneously or extremely dense breasts had the highest interval rate of advanced-stage disease (>0.4 case per 1,000 exams). Just over half of women with heterogeneously dense or extremely dense breasts (51.0 per cent and 52.5 per cent, respectively) had a low 5-year risk; their interval cancer rates were 0.58 to 0.63 case per 1,000 exams and 0.72 to 0.89 case per 1,000 exams, respectively.
The researchers noted that their study did not address the potential benefit of supplemental imaging, alternative imaging strategies, or more frequent mammography. However, they concluded that digital mammography has sufficiently high rates of breast cancer detection and reasonably low false-positive rates and that use of supplemental imaging should not be based only on breast density, since interval cancer rates are not high in all women with dense breasts.
“Primary care providers can calculate 5-year breast cancer risk using the BCSC risk calculator and use this information in their discussions about supplemental or alternative screening methods in women with dense breasts,” the researchers wrote.
The authors of an accompanying editorial said that the study provides “compelling evidence” that breast density should not be the only factor considered in decision making about supplemental imaging and suggests that federal legislation on screening in women with dense breasts is “premature.” The editorialists agreed with the study authors that risk assessment should also factor into supplemental imaging decisions.
“Given the lack of scientific consensus, resources targeted for breast density legislation would be better devoted toward more accurate identification of women at high risk for interval breast cancer, research on optimal use of imaging methods, reduction of disparities in screening and early detection, and training of front-line primary care providers on breast cancer risk assessment,” the editorialists wrote.
The study has been published in Annals of Internal Medicine.
