Karla Kerlikowske, M.D., from the San Francisco Veterans Affairs Medical Center in California, and colleagues analyzed data on the benefits and harms of various mammography frequencies from 11,474 women with breast cancer and 922,624 women without breast cancer.

The researchers found that there was no increase in the risk of large or advanced stage tumors for women 50 to 74 years old with biennial versus annual screening, regardless of breast density or use of postmenopausal hormonal therapy. For women 40 to 49 years old with extremely dense breasts, there was a higher risk of advanced stage cancer (odds ratio, 1.89) and large tumors (odds ratio, 2.39) with biennial versus annual screening. The cumulative probability of a false positive result was lower with biennial screening for women 50 to 74 years old with scattered fibroglandular densities or fatty breasts. The probability was higher for women undergoing annual mammography with extremely dense breasts who were 40 to 49 years old or used estrogen plus progestogen.

"In conclusion, women aged 50 to 74 years, regardless of breast density or hormone therapy use, can undergo biennial rather than annual mammography because biennial screening does not increase the risk of presenting with advanced disease but does substantially reduce the cumulative risk of a false-positive mammography result and biopsy recommendation," Kerlikowske and colleagues write. "Women aged 40 to 49 years with extremely dense breasts who choose to undergo mammography should consider annual screening to decrease the risk of advanced-stage disease but should be informed that annual screening leads to a high cumulative probability of a false-positive mammography result because of the additional screening examinations."

Abstract
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