For decades, estimates of breast cancer overdiagnosis from screening have varied widely, with some studies suggesting that 30-50% of screen-detected cancers would never have caused harm. A new reanalysis of all eight major randomized trials challenges those figures, concluding that the true rate is likely below 5%.
The researchers, from the University of Southern Denmark and collaborators, accounted for differences in follow-up time, screening frequency, and the fact that women in control groups often received screening after trials ended. They also compared trial patterns with real-world data from Denmark, where screening was introduced regionally at different times, allowing a natural comparison.
The findings suggest that previous high estimates were based on incomplete trial data. According to the authors, when interpreted in full temporal context, the trials are consistent with overdiagnosis of less than 5%. This could reassure women considering screening, as the benefits of early detection likely outweigh the small risk of unnecessary treatment.