Mammography Overdiagnosis Estimates May Be Far Too High, Reanalysis Finds
A reanalysis of all eight major randomized mammography trials suggests breast cancer overdiagnosis may occur in under 5% of screened cases. Earlier widely cited figures of 30% to 50% may have been inflated by differences in follow-up duration, screening intervals, and screening after trials ended. The findings could shift how the benefits and harms of population screening are weighed.
Researchers revisited every large randomized mammography screening trial and set those results beside Danish data. Denmark offered a useful comparison because organized screening started in certain areas 17 years before others, letting scientists observe diagnosis patterns as programs rolled out and matured.
Overdiagnosis refers to tumors found by screening that would not have produced symptoms or shortened a woman's life. In trials, diagnoses often rise at first, then fall as earlier detection shifts timing. Screening after trials ended and uneven follow-up can distort this pattern, possibly making overdiagnosis look larger than it is.
If these findings hold, they could influence how women, clinicians, and guideline groups discuss mammography. A lower overdiagnosis estimate may reduce one source of anxiety about screening and could shift how benefits and harms are weighed in public health messages. It may also affect decisions about screening intervals and program design, though individual choices will still depend on personal risk, preferences, and clinical advice.