Their report, published in the New England Journal of Medicine, estimates that in the last 30 years, more than one million women have been overdiagnosed with breast cancer, and that screening with mammography has not resulted in a reduction in late-stage metastatic cancers discovered, a benefit that should have been expected.
They acknowledge that death rates have declined, but they suggest that has more to do with better late-stage breast cancer treatments in recent years, not in increased treatment at earlier stages of disease.
"Our analysis suggests that whatever the mortality benefit, breast-cancer screening involved a substantial harm of excess detection of additional early-stage cancers that was not matched by a reduction in late-stage cancers," they wrote.
"This imbalance indicates a considerable amount of overdiagnosis involving more than 1 million women in the past three decades—and, according to our best-guess estimate, more than 70,000 women in 2008 (accounting for 31% of all breast cancers diagnosed in women 40 years of age or older)."
They argue that the benefits from mammography "are probably smaller, and the harm of overdiagnosis probably larger, than has been previously recognized."