How reliable is the evidence for screening mammography?

Substantial reduction in breast cancer mortality has been proven in randomized trials of screening mammography. These trials have found a statistically significant benefit both for women ages 40-49 years and for women age 50 years and older at onset of screening. In fact, it is likely that the trials actually underestimate the benefit for an individual woman who is screened. Service screening programs have shown a 63% reduction in deaths from breast cancer among women who are screened. Virtually all major medical organizations now advise screening mammography for women ages 40 and older. Two recent studies that questioned the validity of results from screening mammography trials are themselves fatally flawed.