Cancer ResearchBreast Cancer Screening Overdiagnosis May Be Below 5%, Not 30–50% as Long Feared
A new study from the University of Southern Denmark reanalyzed all eight major randomized mammography trials and found that breast cancer overdiagnosis — detecting cancers that would never have caused harm — may be below 5%. Previous estimates suggested 30–50% of screen-detected cancers were overdiagnosed, influencing guidelines worldwide and causing some women to question screening's value. Researchers accounted for follow-up time, screening frequency, and post-trial screening activity that earlier analyses often ignored. Using Denmark's staggered rollout of national screening as a real-world reference, they found patterns consistent with very low overdiagnosis. The findings suggest earlier high estimates were based on immature trial data and flawed methodology, not true overdiagnosis signals. This could meaningfully shift how clinicians and women weigh the risks and benefits of routine mammography.
