Women aged 50 to 74 years who undergo biennial screening mammography face a similar risk of advanced disease and lower risk of false-positive results than those who undergo annual exams, according to a study published online March 18 in the Journal of the American Medical Association. Although the findings apply to women with dense breasts or on hormone therapy, the data are more muddled for women aged 40 to 49 with extremely dense breasts.
When the U.S. Preventive Services Task Force revised its screening mammography guidelines in 2009, the update represented a blanket recommendation that considered only age as a risk factor. Karla Kerlikowske, MD, from the general internal medicine section at San Francisco Veterans Affairs Medical Center, and colleagues sought to clarify the benefits and harms of screening frequencies by age, breast density and postmenopausal hormone therapy use.
The researchers collected data prospectively on 11,474 women with breast cancer and 922,624 without from the Breast Cancer Surveillance Consortium from January 2004 to December 2008.
They categorized screening as annual (nine to 18 months apart), biennial (18 to 30 months apart) or triennial (30 to 42 months apart) and defined advanced stage disease as stages IIb, III or IV and large tumors greater than 20 mm in diameter.
Kerlikowske et al defined a false-positive recall or biopsy recommendation as no invasive carcinoma or ductal carcinoma in situ (DCIS) within one year of a positive screening exam or before the next screening exam.
After calculating odds ratios by comparing the risk of less favorable tumor characteristics by screening interval, the researchers found women aged 50 to 74 years undergoing biennial mammography were not at increased risk compared with those undergoing annual exams, regardless of breast density or hormone therapy use.
Women aged 50 to 74 years with low or average breast density not receiving hormone therapy face a cumulative probability of at least one false-positive mammography result after 10 years of 49.8 percent with annual screening, 30.7 percent with biennial and 21.9 percent with triennial screening, according to the researchers.
“In contrast, women aged 40 to 49 years with extremely dense breasts undergoing biennial compared with annual mammography were at increased risk of advanced stage and large tumor size,” wrote Kerlikowske et al. However, these women also face a higher risk of cumulative false-positive results with annual exams, according to Kerlikowske and colleagues.
Women in this age group undergoing annual screening with heterogeneously dense breasts face a 69.8 percent cumulative 10-year probability of a false positive result; those with extremely dense breasts have a 65.5 percent rate.
The researchers concluded that women aged 50 to 74 years, regardless of breast density or hormone therapy, can undergo biennial rather than annual mammography because the longer interval does not increase the risk of diagnosis of advanced stage disease but does substantially reduce the cumulative risk of a false-positive result and biopsy recommendation. Women age 40 to 49 years with extremely dense breasts require informed decision-making based on the increased risk of advanced diagnosis with biennial screening counter-balanced against the high cumulative probability of a false-positive result with annual exams.