Context

There is no question that breast cancer screening identifies cancers that would never have surfaced in a woman's lifetime in the absence of screening (overdiagnosis). However, high-quality studies are needed to quantify this harm, and this is the main objective of the study by Kalager and colleagues. A review of incidence trends of breast cancers over 20 mm in size (which are by definition considered to be advanced) in seven countries with long-running breast screening found unchanged rates with screening.1 This suggests that the massive increases in early invasive breast cancers and in situ cases seen when breast screening is introduced does not prevent late-stage cancers and is therefore not early detection, but overdiagnosis. It also explains …