A new study offers a reality check to anyone who says a mammogram saved her life. For every woman in whom mammography detected a breast cancer that was destined to become large and potentially life-threatening — the kind that screening is intended to head off — about four are diagnosed with one that would never have threatened their health. But the surgery, chemotherapy, or radiation that follows such diagnoses can be traumatic, disfiguring, toxic, or even life-shortening even as it’s unnecessary.
Prior estimates of how many mammogram-detected cancers are overdiagnoses, meaning they don’t need to be treated, have ranged from 0 to 54 percent. The new study published Wednesday in the New England Journal of Medicine, improves on those by using hard data rather than mathematical modeling, and 40 years of it.
