INCIDENCE AND MORTALITY FROM BREAST-CANCER IN THE MAMA PROGRAM FOR BREAST SCREENING IN FINLAND, 1973-1986

Background. A cohort of women enrolled in the Mama breast self-examina tion-(BSE) containing breast screening program in Finland from 1973 th rough 1975 (with BSE used for screening and mammography for diagnosis) was studied. Methods. Twenty-eight thousand seven hundred eighty-five women who returned calendars recording their practice of BSE over a 2 -year period have been followed by linkage with the records of the Fin nish Cancer Registry through 1986. The incidence of and mortality from breast cancer was compared with that expected in the Finnish populati on based on a model incorporating Finnish national data for breast can cer incidence and case fatality. Results. Breast cancer incidence was higher than expected (a rate ratio of 1.19 over all ages). The stage d istribution of cases was not different from that expected from Finnish cancer registry data for 1980, but the breast cancer mortality was lo wer than expected (a rate ratio of 0.75). The latter difference occurr ed mainly in Years 3-6 of the follow-up period. The effect seemed simi lar in women under and over the age of 50 years. The cohort was of hig her educational status than the Finnish population, and the mortality from all causes was lower than the general Finnish population, an effe ct seen in previous studies of compliers with breast screening. Conclu sions. The reduction in mortality from breast cancer in the study coho rt is consistent with an effect of the BSE-containing Mama program, th ough selection bias, inherent in any observational study of screening, provided an alternative explanation for the findings.