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

A recent study challenges the widely held belief that breast cancer screening significantly overdiagnoses the disease. Overdiagnosis refers to the detection of breast cancers that would never have caused symptoms or threatened a woman's health during her lifetime. For decades, researchers have debated the extent of this phenomenon, with some estimates suggesting up to 50% of cancers detected through screening may be overdiagnosed.

However, a comprehensive analysis of randomized controlled trials has found that the actual rate of overdiagnosis is likely much lower. Researchers at the University of Southern Denmark and Lillebælt Hospital, led by professor Sisse Helle Njor, analyzed data from all available randomized trials of mammography screening programs.

They compared these results with breast cancer incidence data from Denmark, where organized screening began at different times in various regions. By accounting for the timing effects of screening, the researchers found that the initial rise in diagnosed cancers after screening was introduced should be followed by a decline as these cancers would have been detected later anyway.

This pattern suggests that most of the early increase in diagnoses is not overdiagnosis but rather the result of earlier detection. The study's findings indicate that the overdiagnosis rate associated with screening is probably below 5%, not the previously estimated 30-50%. This lower estimate could have significant implications for women considering breast cancer screening.

By providing a more accurate picture of the risks and benefits, the study aims to help women make informed decisions about participating in screening programs.