Mammograms may not be better at preventing deaths from breast cancer than physical breast exams alone, according to one of the largest studies on mammography.
The study followed 90,000 women in Canada between the ages of 40 and 59 for 25 years. Half of the women were randomly assigned to get mammograms, while the other half did not. All women in the mammography half and women aged 50-59 in the no-mammography control group received yearly physical breast examinations. Women aged 40-49 had one breast exam followed by typical care with their usual physicians.
Researchers found that there was no difference in death rates between women who underwent mammography screening and women who did not. They also reported that 22% of invasive breast cancers that were detected by mammography were over-diagnosed and would not have resulted in death or required treatment with chemotherapy, radiation or surgery even if they had not been found.
The New York Times reported that the American Cancer Society has convened an expert panel to review the data for and against mammography screening, which will likely issue revised guidelines later this year. Multiple prior studies have shown that mammography can reduce death rates from breast cancer.
The efficacy and frequency of mammography screening has been hotly debated in recent years, with current recommendations varying by country and organization. The U.S. Preventative Services Task Force (USPSTF) currently recommends women get mammograms every two years between ages 50 and 74, while the American Cancer Society advises women get screened every year starting at age 40.