Cancer Screening: Opinions from the Field
April 16, 2012
By LISA M. SCHWARTZ, M.D. and STEVEN WOLOSHIN, M.D.
Since there is no reliable way to know whether a screening-detected cancer represents overdiagnosis, most people seek treatment. People on the receiving end of overdiagnosis can only be harmed — sometimes seriously — by unnecessary surgery, radiation and chemotherapy. While it’s hard to precisely estimate the amount of overdiagnosis that occurs, most experts agree that it’s an inevitable consequence of screening.
The bottom line is that while screening may help some people avoid a cancer death, it will harm many others…
As noted by the task force, the harms of P.S.A. screening probably outweigh the benefits, which actually are uncertain. None were observed in an American trial, and just a small benefit was found in a European trial. The test results in a disturbing amount of overdiagnosis.
For women at average risk, mammography is a close call. Trials suggest that there are about one to three fewer deaths for every 1,000 women screened over 10 years (the benefit increases with age). But there is substantial overdiagnosis — as many as 10 unnecessary diagnoses per death avoided. Rather than persuading women to be screened, we should help them be informed.
For colon cancer screening, the benefit of the fecal occult blood test outweighs the harms. (Surprisingly, colonoscopy hasn’t been evaluated yet in a randomized trial.) There are about three fewer colon cancer deaths per 1,000 people screened over 13 years, without a lot of false alarms requiring invasive procedures. There has been no evidence of cancer overdiagnosis with this test.