Overdiagnosis of Invasive Breast Cancer with Screening Mammography

Much attention has been focused on overdiagnosis when screening for prostate cancer, but how common is overdiagnosis with screening mammography? In Norway, a mammography screening program was gradually implemented region by region over a decade, beginning in 1996. Using a complex methodologic approach, researchers compared breast cancer incidence in regions and periods before program initiation with the incidence after initiation of mammography screening to estimate rates of overdiagnosis. Ductal carcinoma in situ was not studied, given its differing clinical course.

Nearly 40,000 cases of invasive breast cancer were diagnosed during the decade. For every 2500 women invited to undergo mammography screening, estimates indicated that 20 cases …