Mammography Screening

A widely quoted study in the February 11, 2014 issue of BMJ concluded that annual mammography in women 40-59 years old does not reduce mortality from breast cancer. This was not a new study, and its design was complex. It was a 25-year follow-up of the Canadian National Breast Screening Study, which started in 1980. The 89,835 participants, who were recruited, had a physical breast examination and then were randomized to four rounds of annual mammography and physical examination, or usual care, if they were 40-49 years old, or to mammography plus physical exam, or physical exam alone, if they were 50-59 years old. During the entire study period, 505 women randomized to mammography and 500 randomized to no mammography died of breast cancer.

The February 18 issue of BMJ published readers’ responses to the study, which were mostly critical of its design and execution. One criticism repeated by several writers was that women who had tumors detected at the initial physical exam were directed (for their own good, presumably) into the mammography group (the authors specifically deny this). Another was that the quality of the mammography studies was poor. It seems fair to assume that the quality of mammography has improved since the 1980’s. Digital mammography, which has replaced film screen mammography in more than 70% of mammography centers in the US, is more accurate than film mammography in women <50 years of age and in women of any age with dense breasts.

Our most recent publication on cancer screening, in the December 2012 issue of Treatment Guidelines from The Medical Letter, reported that the American Cancer Society, the American College of Obstetricians and Gynecologists, the Society of Breast Imaging and the American College of Radiology recommend yearly mammograms starting at age 40 for women at average risk. The US Preventive Services Task Force recommends screening mammography every 2 years, and only for women 50-74 years old. Will any of those organizations change their recommendations as a result of the Canadian study? I doubt it.

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  1. Clifford Dacso, MD says:

    When authorities disagree, all on valid interpretation of well conducted studies, I present the data to my patients, disclose the problems inherent in the studies (and studies in general,) make my recommendation, and abide by the patient’s decision. Population-based large studies can only provide guidance; they can not be prescriptive as a consequence of individual variation, I believe.

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