New study suggests most women with breast cancer were not saved by mammograms, despite beliefs


October 26, 2011

The probability that a woman with screen-detected breast cancer avoids dying from the disease because of mammography is just 13%, according to a study published this month in the Archives of Internal Medicine.  This contradicts the popular belief that routine screening will "save my life."

In this recent analysis, researchers from Dartmouth used the National Cancer Institute's software for analyzing Surveillance Epidemiology and End Results (SEER) data to estimate the probability that a woman with screen-detected breast cancer has had her life saved because of screening.  They did so by estimating the risk of dying from breast cancer in the presence and absence of mammography for various ages (ages 40, 50, 60, and 70 years).  To measure the downstream benefits of screening, they estimated the 10-year risk of diagnosis and the 20-year risk of death.  The researchers assumed that approximately 60% of all breast cancers are detected by screening mammograms based on data from the 2003 National Health Interview Survey. 

The results suggest that the probability that a woman with screen-detected breast cancer benefited from screening is always less than 25%.  Among the women with breast cancer who detected the disease by screening, only about 3 - 13 percent of them were actually helped by the test.  To sum up their findings, the authors write, "Earlier diagnosis (either via enhanced awareness or screening) and better treatment are clearly part of the explanation for this large survivor population. But so too is the enthusiasm for screening and the resulting overdiagnosis. And, ironically, this enthusiasm may, in turn, be the product of a large number of survivors. This self-reinforcing cycle (the more detection, the more enthusiasm—the so-called popularity paradox of screening) is driven, in part, by the presumption that every screen-detected breast cancer survivor has had her "life saved" because of screening. Our analyses suggest this is an exaggeration." More on the study in this NY Times article.

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