- Kenny Lin, MD, MPH
Providing preventive services is a core responsibility of family medicine, and, consequently, AFP devotes many pages to keeping readers up-to-date with the latest studies and recommendations on breast cancer screening. There has been much news of note in the past few years, beginning with the U.S. Preventive Services Task Force's 2009 statement that clinicians should engage women in shared decision-making discussions about the relative benefits and harms of beginning screening mammography before age 50, and perform screening only every other year.
Other groups, such as the American College of Obstetricians and Gynecologists, recommend annual mammography starting at age 40. As reviewed in a recent AFP article, the conflicting USPSTF and ACOG guidelines agree that mammography appears to lower breast cancer mortality, but dispute how to value the harms: false positive results, anxiety, biopsies, overdiagnosis, and unnecessary treatment. To further complicate matters, as adjuvant therapies for breast cancer continue to improve, researchers have speculated (with some supporting data) that mammography may not be nearly as useful at preventing deaths from breast cancer today as it seemed to be a generation ago.
But could the mortality benefit of mammography in younger women actually be as low as zero? That was the startling conclusion of the Canadian National Breast Screening Study, which published its 25-year follow-up report last week in BMJ. Beginning in the early 1980s, this randomized trial evaluated the effect of 5 years of annual mammography in nearly 90,000 women between the ages of 40 and 59 and found no difference in breast cancer mortality between the intervention and control groups. (It's important to note that women age 50 and older in the control group received annual clinical breast examinations.) The study's findings also suggested that more than 1 in 5 breast cancers detected in the mammography group would not have become clinically evident during a patient's lifetime in the absence of screening.
The American College of Radiology immediately labeled the BMJ study "incredibly flawed and misleading" and advised that clinicians and patients disregard its findings. Others countered that this study's well-documented limitations (e.g., older mammography technology) were no more disqualifying than those of other (even older) studies that found screening reduced breast cancer deaths: "If you’re not going to be swayed at all by a randomized controlled trial of 90,000 women with 25 year follow up, excellent compliance, and damn good methods, it might be time to consider that there’s really no study at all that will make you change your mind [about the effectiveness of screening mammography]."
Researchers recently estimated in Annals of Internal Medicine that the total cost of mammography screening in the U.S. in 2010 was $7.8 billion, not including costs of missed work or subsequent treatments. If 85% of women between the ages of 40 and 85 were screened annually as recommended by ACOG, the cost would have been $10.1 billion. In contrast, if the same proportion of women adhered to USPSTF screening guidelines (biennial mammography between 50 and 74, with the option of starting earlier or ending later based on a woman's preferences and health status), the cost would have been $3.5 billion. Even though the Affordable Care Act requires insurers to cover annual screening mammography in women over 40 without any out-of-pocket costs, are patients really getting their money's worth in improved health?