Overdiagnosis in the population-based service screening programme with mammography for women aged 40 to 49 years in Sweden

Abstract

To estimate the level of overdiagnosis of all breast cancers and of invasive breast cancers in women aged 40-49 invited to the subsequent screening rounds in the Swedish service-screening programme 1986-2005. To estimate the level of overdiagnosis in subsequent screening, the rate ratios (RR) of the breast cancer incidence in the study group (women in areas with screening in ages 40-49) and the control group (women in areas with no screening in ages 40-49) were calculated for all breast cancers and for invasive breast cancers. The RR estimates were adjusted for the prescreening difference in incidence between study and control group and for lead time. The prescreening incidence rate ratio was estimated at 0.92 (95% confidence interval [CI]: 0.88-0.97). The number of breast cancer cases and person-years were 6047 and 3.8 million, and 7790 and 5.2 million, in the study group and control group respectively during the study period. The RR estimate for all cancers was 1.01 (95% CI: 0.94-1.08) when adjusted for prescreening difference and a lead time of 1.2 years. The corresponding estimate for invasive breast cancers was 0.95 (95% CI: 0.88-1.02). We found no significant overdiagnosis for women aged 40-49 in the Swedish service screening programme with mammography.