Data-rich modeling suggests many women need breast screening only triennially

Average-risk women with low breast density who get screened for breast cancer every three years share a trait in common with higher-risk women with high breast density who get screened every year.

Both groups will maintain a similar or better balance of benefits and harms than average-risk women who get screened every other year.

That’s according to a study published this week in Annals of Internal Medicine.

The researchers used simulation modeling drawn from national incidence, breast density and screening performance data to estimate outcomes for various screening intervals after age 50 years based on breast density and risk for breast cancer.

First co-authors Amy Trentham-Dietz, PhD, of the University of Wisconsin and Karla Kerlikowske, MD, MS, of UC-San Francisco and colleagues zeroed in on women aged 50 years or older with various combinations of breast density and relative risk of 1.0, 1.3, 2.0 or 4.0.

(A relative risk of 1 indicates that there is no increased risk; a relative risk of 4 indicates a fourfold increase in risk.)

They limited their study to one modality: digital mammography.

The interventions the team considered were annual, biennial or triennial digital mammography screening from ages 50 to 74 years (vs. no screening) and ages 65 to 74 years (vs. biennial digital mammography from ages 50 to 64 years).

The measurements they used were lifetime breast cancer deaths, life expectancy and quality-adjusted life-years (QALYs), false-positive mammograms, benign biopsy results, overdiagnosis, cost-effectiveness and ratio of false-positive results to breast cancer deaths averted.

Among their key findings:

• Screening benefits and overdiagnosis increase with breast density and relative risk.
• False-positive mammograms and benign results on biopsy decrease with increasing risk.
• Among women with fatty breasts or scattered fibroglandular density and a relative risk of 1.0 or 1.3, breast cancer deaths averted were similar for triennial versus biennial screening for both age groups.
• Breast cancer deaths averted increased with annual versus biennial screening for women aged 50 to 74 years at all levels of breast density and a relative risk of 4.0. So too for those aged 65 to 74 years with heterogeneously or extremely dense breasts and a relative risk of 4.0.

“However, harms were almost twofold higher,” the authors write of the latter finding. “Triennial screening for the average-risk subgroup and annual screening for the highest-risk subgroup cost less than $100,000 per QALY gained.”

The authors acknowledge as a limitation their models’ exclusion of women younger than 50, those with a relative risk less than 1 and imaging methods other than digital mammography.

The study has caught the eye of the mainstream press. Kerlikowske told the Los Angeles Times that the team’s simulation models “are very applicable to the populations we screen.”