A major concern with screening women for breast cancer biennially (every two years)—as guidelines from the U.S. Preventive Services Task Force and American Cancer Society (ACS) now recommend—rather than annually is that it will delay cancer diagnosis until tumors are at a more dangerous stage and will thus endanger women’s lives. Several studies have suggested that this is not the case and that biennial mammograms produce far fewer false-positives and unnecessary biopsies than annual screening, though this may not be true for premenopausal women.
- In a 2011 study of women ages 40 to 59 in the Annals of Internal Medicine, 61 percent of those who were screened annually for a decade had at least one false-positive result, compared to only 42 percent of those tested every other year (who required one-third fewer biopsies). Reassuringly, women screened every two years were not significantly more likely to be diagnosed with late-stage cancer than those screened annually.
- In a study in JAMA Internal Medicine in 2013, women ages 50 to 74 who had mammograms every two years were no more likely to be diagnosed with advanced-stage or large-size tumors than those screened annually, but had a much lower risk of false-positive results. In contrast, among women in their forties, the study found that those with very dense breasts had higher rates of advanced breast cancer when screened every two years instead of annually, along with a greatly increased risk of false-positives.
- The most recent study, commissioned by the ACS and published in JAMA Oncology in 2015, found that postmenopausal women (not using hormone therapy) diagnosed with breast cancer had a similar proportion of advanced or large tumors whether they had annual or biennial mammograms. However, premenopausal women were more likely to have advanced or large tumors following biennial screening, though the researchers said they didn’t have data to determine if this would result in increased breast cancer mortality. This study contributed to the decision of the ACS to continue to recommend annual screening up to age 55, by which time the great majority of women are past menopause.