An editorial (pdf file - pages 3 & 4) in the BMJ this week comments on the "muted" reaction to the new guidelines on screening mammography for women in their 40s that were released by the American College of Physicians in April. Rather than calling for universal screening, they recommend that women make an informed decision after learning about the benefits and harms of mammography.
The authors support the guidelines because, they say, no right choice exists and because screening has mixed effects – some women will benefit (by avoiding death from breast cancer) but others will be harmed by unnecessary treatment. So the next step is to ensure that women understand what is likely to happen if they do or do not undergo screening.
The authors say that for every 1000 women screened over the next 10 years less than one life will be “saved” for younger women and about three lives will be saved for older women.
But screening has several harms, say the authors. False positives – abnormalities detected at mammography that often cause women to undergo repeat testing (or perhaps biopsy) to rule out cancer - are the most familiar and can cause short term anxiety, inconvenience, and sometimes unnecessary biopsies. But they think that overdiagnosis is the most important harm of screening.
Overdiagnosis is the detection of lesions that meet the pathological criteria for cancer but would not progress to cause symptoms or death, they explain. Women who are overdiagnosed can only be harmed by treatment – they cannot benefit because no treatment was needed. Harms include disfiguring surgery, side effects of chemotherapy or hormonal therapy (such as nausea, fatigue, and hair loss), and injury from radiation.
Calculating the chance of overdiagnosis is challenging, but the authors estimate that, for every 1000 women screened over the next 10 years, up to five aged 40-49 and up to nine aged 50 and over may be affected.