Biennial mammography initiated at age 50 achieved most benefits of annual screening

Cancer Intervention and Surveillance Modeling Network examined 20 screening strategies.

An analysis of 20 screening strategies using various mammography screening schedules and age groups suggests that biennial screening for women aged 50 to 74 provides nearly all the benefits of annual screening with fewer false-positives.

These data were published simultaneously in Annals of Internal Medicine with the U.S. Preventive Services Task Force breast cancer screening guidelines update, which recommends biennial screening after age 50 and recommends against screening before age 50. Researchers from the Cancer Intervention and Surveillance Modeling Network of the National Cancer Institute developed six models of breast cancer incidence and mortality to examine 20 screening strategies with different schedules for beginning and ending mammography screening. The models included national data on age-specific breast cancer incidence, mortality, mammography characteristics and treatment effects.

Across the models, screening biennially yielded 67% to 99% of the benefits of annual screening — an average of 81%. Screening biennially also led to a reduction in false-positive results by nearly half. The researchers also reported that screening biennially from ages 50 to 69 led to a median 16.5% reduction in breast cancer deaths compared with no screening.

Initiating biennial screening at age 40, compared with age 50, reduced mortality by another 3% (range, 1% to 6%); however, screening at this age also used more resources and led to more false-positive results, according to the CISNET resaserchers. The researchers also reported that annual screening from age 40 to 69 would lead to 2,250 false-positive results for every 1,000 women screened — almost double that found with biennial screening in this age group. In addition, 7% of women who receive false-positives results would undergo an unnecessary biopsy.

If screening begins at age 40 and is performed every other year, mortality reduces by a median 19.5% compared with beginning screening at age 50, but false-positives, unnecessary biopsies and anxiety increase.

The researchers wrote that biennial screening after age 69 led to further reductions in mortality across all models, but over diagnosis was most common in the older age groups.

They observed consistent results across the six models. “While the findings represent a comprehensive review of existing data, the decisions about the best screening strategy depend on individual and public health goals, resources and tolerance for false-positive mammograms, unnecessary biopsies and over diagnosis,” study author Jeanne S. Mandelblatt, MD, MPH, of Georgetown Lombardi Comprehensive Cancer Center, said in a press release. She also called for more research to understand how to tailor screening based on individual risk.

Mandelblatt JS. Ann Intern Med. 2009;151:738-747.