On the Efficacy of Screening for Breast Cancer
"Mammography" (screening for breast cancer by x-rays) came to be widely accepted in the 1980s, when a number of clinical trials demonstrated a substantial reduction in risk. Early detection, before the disease spreads, permitted therapy that was less invasive and more effective. Questions that remained were largely about efficacy for younger women, and optimal frequency for older women. The consensus was challenged in a series of papers by two researchers at the Nordic branch of the Cochrane collaboration, who concluded that mammography does not save lives: instead, it exposes women to unnecessary surgical procedures. The basis for the critique turns out to be simple. Studies that found a benefit from mammography were discounted as being of poor quality. The remaining negative studies were combined in a meta-analysis. The critique therefore rests on judgments of study quality. These are based on misreadings of the data and the literature. In our view, the critique has little merit, and the prior consensus on mammography was correct.