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Dense breasts alone may not justify additional screening for breast cancer
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Dense breast tissue alone may not correspond with a higher risk for interval breast cancer and, thus, should not be considered the sole criterion for supplemental imaging, according to study results.
Twenty-one states mandate that women with dense breasts — which can increase the risk for breast cancer and hide tumors — are notified and advised to discuss supplemental imaging with their doctor, according to study background. Further, between 42% and 45% of women screened will have dense breast tissue, according to a press release.
Karla Kerlikowske
“You cannot do supplemental screening for 45% of the population,” Karla Kerlikowske, MD, professor of medicine and epidemiology/biostatistics at the University of California, San Francisco, said in a press release. “It is just not realistic, neither from a time or cost standpoint.”
Kerlikowske and colleagues used data from the Breast Cancer Screening Consortium (BCSC) mammography registries to identify 365,426 women aged 40 to 74 years who underwent 831,455 digital screening mammography examinations. Researchers excluded women with a history of breast cancer or breast implants, women who underwent unilateral mammography and women receiving their first mammography screening.
Researchers classified breast density using the Breast Imaging Reporting and Data System (BI-RADS) categories, which included almost entirely fat, scattered fibroglandular densities, heterogeneously dense or extremely dense classifications. They also used the BCSC risk calculator to determine patients’ 5-year risk for invasive cancer and categorized risk as low (0% to <1%), average (1% to 1.66%), intermediate (1.67% to 2.49%), high (2.5% to 3.99%) and very high (≥ 4%). Researchers considered a 5-year risk of 0% to 1.66% low to average.
Researchers sought to measure the interval cancer rate — or invasive cancer less than 12 months after a normal mammography results — per 1,000 mammography examinations. A high interval cancer rate indicated more than one case per 1,000 examinations.
The analysis focused on the detection of invasive cancers due to the high detection rate of ductal carcinoma in situ by mammography, according to the researchers.
Approximately 47% of women screened had dense breasts. The highest BCSC 5-year risk occurred among women with heterogeneously or extremely dense breasts; however, 51% of women with heterogeneously dense breasts and 52.5% of women with extremely dense breasts exhibited low to average 5-year risk.
Overall, 2,696 cases of invasive cancer occurred within 12 months of screening mammography. Researchers associated invasive cancer with older age, white race, heterogeneously or extremely dense breasts, BCSC 5-year risk of 1.67% or greater and a family history of breast cancer.
High interval cancer rates occurred among women with a 5-year breast cancer risk of 1.67% or greater and extremely dense breasts (47.5% of women with extremely dense breasts), as well as among women with a breast cancer risk of 2.5% or greater and heterogeneously dense breasts (19.5% of women with heterogeneously dense breasts). These subgroups comprised 24% of women aged 40 to 74 years with dense breasts and 12% of women undergoing mammography.
Women aged 40 to 49 years exhibited average interval cancer rates of less than one case per 1,000 examinations regardless of breast density.
Among women with low to average breast cancer risk, those with heterogeneously dense breasts had interval cancer rates of 0.58 to 0.63 and those with extremely dense breasts had interval cancer rates of 0.72 to 0.89 case per 1,000 screening examinations.
The highest interval rates of advanced-stage invasive cancer (> 0.4 case per 1,000 examinations) occurred among women with a 2.5% or greater 5-year risk and heterogeneously or extremely dense breasts, which represented 21% of women aged 40 to 74 years with dense breasts. Women aged 60 to 74 years with extremely dense breasts (3% of these women) exhibited elevated rates of interval advanced-stage disease.
Researchers observed low false-positive rates across age and breast density groups, with the exception of women aged 40 to 49 years with scattered fibroglandular densities or heterogeneously dense breasts.
The researchers acknowledged their inability to assess the benefit of supplemental imaging as a study limitation.
“People right now are looking at density reports from mammograms and not taking into account age and other factors,” Kerlikowske said. “You have to look at the risk factors together.”
Laws mandating additional screening requirements for women based on breast density alone may not be warranted, Nancy C. Dolan, MD, and Mita Sanghavi Goel, MD, MPH, wrote in an accompanying editorial.
“This finding suggests that federal legislation on management of screening in women with dense breasts is premature,” Dolan and Goel wrote. “If enacted, such legislation would require significant additional breast cancer screening resources for a large portion of the screening population, with high costs and unclear long-term benefit. Incorporating a risk assessment, such as the BCSC 5-year risk, into the mammography report in addition to breast density information might help clarify risk and improve physicians’ ability to effectively counsel patients on appropriateness of supplemental screening.” – by Cameron Kelsall
Disclosure: Kerlikowske reports no relevant financial disclosures. Please see the full study for a list of all other researchers’ relevant financial disclosures. Goel reports receiving a grant from The Avon Foundation.
Perspective
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Richard L. White Jr., MD, FACS
When nearly 50% of all women undergoing screening mammography have dense breasts, a policy of supplemental imaging in all of these women is impractical and fiscally untenable. Kerlikowske and colleagues nicely address the notion of who is most likely to benefit from supplemental imaging. The paper provides detailed information regarding the sensitivity of screening mammography in a variety of populations based on age, breast density and risk strata. The authors test six practical strategies for additional imaging to assess the utility in each group. Although they do not provide an assessment of the utility of supplemental imaging, their analysis suggests potentially useful methods for stratification.The care of women with breast cancer and at risk for breast cancer has become increasingly complex as we begin to understand that breast cancer is not one monotonous entity but a complex array of genetic rearrangements. In this setting, our view of screening of necessity becomes more nuanced.
Kerlikowske and colleagues have — with limitations — begun a discussion employing robust data and reasonable statistical modeling. Randomized trials in this setting are unlikely to move forward given prohibitive costs and the urgency of identifying better practices in real time. The emphasis on risk assessment using straight forward modeling makes practical the notion of “discuss your risks with your primary physician.”
Which women with dense breasts should undergo supplemental imaging? The proposed model is as good as any proposed to date despite the limited data on the efficacy of supplemental screening.
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