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Breast cancer risk, breast density useful in guiding mammogram frequency

Tailoring mammography screening intervals to each patient will help in maximizing benefits and minimizing harms, according to findings published in the Annals of Internal Medicine.

Researchers found that women with average breast cancer risk and low breast density should have mammograms every 3 years, while women with higher risk and high breast density should be screened yearly.

Amy Trentham-Dietz, PhD, from the University of Wisconsin-Madison Carbone Cancer Center, and colleagues wrote that previous screening recommendations lacked data that would allow both patients and physicians to make personalized decisions.

"To fill this gap, the Cancer Intervention and Surveillance Modeling Network, collaborating with the Breast Cancer Surveillance Consortium (BCSC) (a longstanding network of six U.S. breast imaging registries with links to tumor and pathology registries), used three well-established models to evaluate various screening intervals for digital mammography among subgroups of women based on age, risk, and breast density," they wrote. "Outcomes were projected for women aged 50 (or 65) years who were deciding whether to initiate (or continue) biennial screening until age 74 years or to have annual or triennial screening."

The researchers investigated four screening strategy intervals (annual, biennial, triennial and no screening) along with four breast density levels defined by the American College of Radiology's Breast Imaging Reporting and Data System (BI-RADS): (a, almost entirely fat; b, scattered fibroglandular density; c, heterogeneously dense; and d, extremely dense). They also used four relative risk (RR) levels that incorporated common risk factors, such as postmenopausal obesity, history of benign breast biopsy results and history of lobular carcinoma in situ (1, average risk; 1.3; 2, and 4).

Trentham-Dietz and colleagues measured breath cancer deaths avoided, life-years gained, quality-adjusted life-years gained, cost, false-positive mammograms, benign biopsies and overdiagnosis.

The researchers found that as risk increased, false-positive mammograms and benign biopsy results decreased. In addition, as breast density and RR increased, screening benefits and overdiagnosis increased.

Results showed that both triennial and biennial screening prevented a similar number of breast cancer deaths in women with RR of 1 or 1.3 and fatty or scattered fibroglandular density breasts in women aged 50 to 74 years (median of 3.4 to 5.1 vs. 4.1 to 6.5 deaths averted) and women aged 65 to 74 years (median of 1.5 to 2.1 vs. 1.8 to 2.6 deaths averted).

Annual screening increased the number of preventable breast cancer deaths when compared to biennial screening in women aged 50 to 74 years with RR of 4 and any level of breast density as well as in women aged 65 to 74 years with RR of 4 and heterogeneously or extremely dense breasts. Trentham-Dietz and colleagues reported that harms were nearly two times higher, however.

In addition, it cost less than $100,000 per quality-adjusted life-year to screen average-risk patients triennially and highest-risk patients annually.

"Overall, this comparative modeling study illustrates consistent patterns in benefits and harms that could be useful for guiding shared decision making and tailoring screening intervals," Trentham-Dietz and colleagues concluded. "The results show that for all screening intervals, benefits and harms change with risk and breast density. Further, the threshold to decide on the screening interval will depend on individual preference. Assessing breast density and breast cancer risk can identify subgroups of average-risk women with low breast density who can consider triennial screening and higher-risk women with high breast density who may benefit from annual screening."

In an accompanying editorial, Christine D. Berg, MD, from Johns Hopkins Medicine, wrote that "tailoring one's recommendation based on individualized risk and individualized harm becomes increasingly important" as personalized medical interventions become more mainstream.

"The USPSTF made a grade B recommendation for biennial mammography screening in average-risk women aged 50 to 74 years," she wrote. "This current work from the well-regarded Cancer Intervention and Surveillance Modeling Network and BCSC investigators helps women and clinicians to possible individualize screening frequency based on risk and BI-RADS categories. It will be important to track outcomes in women who undergo alternative screening frequencies to validate this approach." – by Chelsea Frajerman Pardes

Disclosures: Trentham-Dietz reports grants from NCI during the conduct of the study. Please see the full studies for a complete list of all other authors' relevant financial disclosures.