Overdiagnosis in mammography screening: a 45 year journey from shadowy idea to acknowledged reality

Summary box

• Clinical context—Breast cancer is the most common cancer in women worldwide with a significant burden of morbidity and mortality in developed and developing countries.

• Diagnostic change—Mammography screening has provided expanded opportunities to detect breast cancer over the last three decades, and more recently through incremental improvements in detection provided by digital mammography and tomosynthesis

• Rationale for change—Mammography screening can detect breast cancer earlier, leading to improved patient outcomes

• Leap of faith—The benefits of early detection and treatment of breast cancer (lives saved) far outweigh the adverse physical and psychosocial effects of early detection and treatment

• Impact on prevalence—Breast cancer incidence has increased significantly in recent decades, most strikingly among women aged 50-69 years in countries where there is good uptake of mammography screening

• Evidence of overdiagnosis—Strong increases in the incidence of early breast cancer without proportionate reductions in advanced cancer incidence, and evidence from randomised trials and observational studies showing excess cancers detected among women during screening which are not compensated by decrements in incidence once women cease screening

• Harms of overdiagnosis—All women diagnosed with early breast cancer are treated comprehensively for breast cancer, even though some have overdiagnosed (harmless) cancers; these women cannot benefit from treatment but are exposed to the physical and psychosocial harms of cancer treatments

• Limitations—High quality evidence about overdiagnosis and overtreatment in the context of contemporary breast cancer screening and treatment is extremely limited, leading to divisive debates between experts

• Conclusion—Agreement between experts about overdiagnosis in breast cancer screening is urgently needed so that women can be better informed; advances in mammographic technology should be restrained until incremental net improvements in health outcomes …