John Allen Paulos: Cancer by the Numbers
PHILADELPHIA - It is difficult to communicate medical risk to a large audience, especially when official recommendations conflict with emotional narratives. That is why, when the United States Preventive Services Task Force (USPSTF) in 2009 presented its guidelines for breast cancer screening, which recommended against routine screenings for asymptomatic women in their 40's and biennial, rather than annual, mammograms for women over 50, the public responded with confused fury.
The key to understanding this response is to be found in the nebulous zone between mathematics and psychology. People's discomfort with the findings stemmed largely from faulty intuition: if earlier and more frequent screening increases the likelihood of detecting a possibly fatal cancer, then more screening is always desirable. If more screening can detect breast cancer in asymptomatic women in their 40's, wouldn't it also detect cancer in women in their 30's? And, if so, why not, reductio ad absurdum, begin monthly mammograms at age 15?
The answer, of course, is that such intensive screening would cause more harm than good. But striking the proper balance is challenging. Unfortunately, it is not easy to weigh breast cancer's dangers against the cumulative effects of radiation from dozens of mammograms over the years, the invasiveness of biopsies, and the debilitating impact of treating slow-growing tumors that would never have proven fatal.
The USPSTF recently issued an even sharper warning about the prostate-specific antigen test for prostate cancer, after concluding that the test's harms outweigh its benefits. Chest X-rays for lung cancer and Pap tests for cervical cancer have received similar, albeit less definitive, criticism.