A major risk of breast cancer screening may have been overestimated for decades

Breast cancer screening can sometimes identify cancers that would never have caused symptoms or threatened a woman's health during her lifetime. This phenomenon is known as overdiagnosis, and it has long been considered one of the potential drawbacks of screening.

For decades, researchers have debated how often overdiagnosis actually occurs. Estimates from randomized trials have differed sharply, with some studies suggesting that 30-50% of breast cancers detected through screening could fall into this category. Those figures have influenced international discussions about both the benefits and possible harms of population-based breast cancer screening.

"The aim of our study was to bring together the evidence from all randomized controlled trials to get a clearer picture of the extent of overdiagnosis in breast cancer screening," says Sisse Helle Njor, professor at University of Southern Denmark and Lilleb lt Hospital. She continues: