Programme sensitivity and effectiveness of mammography service screening in Helsinki, Finland

Objectives: To evaluate the effectiveness of mammography service screening. Setting: Helsinki (population 0.5 million), the capital of Finland, the breast cancer service programme was started gradually in 1986. Materials and methods: The study was based on the data from the breast cancer programme in Helsinki. All incident cases of breast cancer and rates in the female population in sinki during the period 1970-97, and information on the subsequent breast cancer mortality derived from the files of the Finnish Cancer Registry. To estimate the sensitivity of the programme, number of screen detected cancers were compared with the overall number of breast cancers at targeted age groups. Effects of screening were estimated for cumulative incidence and for the mortalities among the birth cohorts screened. Results: Altogether 144 400 invitations had been sent during 1986-97 among the 50-9 year women as targeted in Helsinki. The average attendance rate was 82%; and 545 breast cancers detected by screening, with a detection rate of 0.46%. In the birth cohort of women born between start of 1935 and the end of 1939-namely, those subjected to most complete screening and long low up time since the onset of the programme-there was an increase in the cumulative incidence breast cancer (relative risk (RR) 1.18, 95% confidence interval (95% CI) 1.09 to 1.27). The sensitivity of the screening programme was 58%; and 53% if corrected for overdiagnosis. There also a decrease of 19% (RR 0.81, 95% Cl 0.62 to 1.05) in the refined mortality within this birth cohort, compared with the death rate of women of comparable ages in the reference cohort. Conclusion: The study provides further support to the hypothesis that service screening with mammography reduces the risk of breast cancer mortality.