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Study finds annual mammography screening produces many false-positives

October 18, 2011

After 10 years of annual screening, more than half of women will receive at least one false-positive recall, according to results of a prospective cohort study published this month in Annal of Internal Medicine.  The results of this study suggest that biennial screening greatly reduces the number of women called back for a second mammogram and unnecessary biopsies.

Researchers analyzed data from seven mammography registries of the Breast Cancer Surveillance Consortium.  The analysis consisted of 169,456 women who underwent first screening mammography at age 40 to 59 years between 1994 and 2006 and 4,492 women with incident invasive breast cancer diagnosed between 1996 and 2006.  The researchers compared the cumulative probability of false-positive recalls and biopsy recommendations, and the stage distribution of incident cancers after 10 years of biennal versus annual screening.  Few women underwent screening over the entire 10-year period.

The cumulative probability of a woman receiving at least one false-positive recall after 10 years was 61.3% (95% CI, 59.4% to 63.1%) with annual and 41.6% (95% CI, 40.6% to 42.5%) with biennial screening in women who started screening at age 40. The cumulative probability of false-positive biopsy recommendation was 7.0% (95% CI, 6.1% to 7.8%) and 4.8% (95% CI, 4.4% to 5.2%) annual and biennial screening, respectively. Estimates were similar when screening began at age 50 years.  There was a small increase in the proportion of late-stage cancers in women who screened biennially compared to annually, with absolute increases of 3.3 percentage points for women aged 40-49 and 2.3 percentage points for women age 50-59.  However, these differences were not statistically significant.  The authors write that "women and physicians should be aware of the possibility of these harms associated with different screening intervals so they can make informed decisions about screening and be prepared for what to expect when they receive their results."