Ideally, screening mammography detects small breast cancers so that they can be removed before they grow, metastasize, and kill. To tell whether screening is succeeding, researchers from Harvard and Dartmouth looked at the rates of mammography, the diagnosis of small breast cancers, large breast cancers, and breast cancer deaths in 16 million women 40 or older in the United States from 2000 through 2010. They found that when mammography rates increased 10%, the number of small cancers detected went up 25%, and the number of large cancers increased by 7%. There was no decline in breast cancer deaths. They concluded that mammography is finding—and women are being treated for—small cancers that may not progress to invasive disease or metastasize to other parts of the body.
The results, which were published online July 6, 2015, by JAMA Internal Medicine, echo those of earlier findings. They underscore a dilemma facing women and their doctors: To get annual mammograms and risk being treated for a tumor that may never become harmful, or have mammograms less frequently and risk missing a cancer until it is larger. The U.S. Preventive Services Task force recommends having a mammogram every one to two years for women ages 50 to 79. The American Cancer Society suggests annual mammograms beginning at age 40. You may want to discuss your personal risk profile, and your preferences, with your doctor.