Incidence and mortality from breast cancer in the Mama Program for Breast Screening in Finland, 1973-1986

A cohort of women enrolled in the Mama breast self-examination-(BSE) containing breast screening program in Finland from 1973 through 1975 (with BSE used for screening and mammography for diagnosis) was studied.

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 Finnish Cancer Registry through 1986. The incidence of and mortality from breast cancer was compared with that expected in the Finnish population based on a model incorporating Finnish national data for breast cancer incidence and case fatality.

Breast cancer incidence was higher than expected (a rate ratio of 1.19 over all ages). The stage distribution of cases was not different from that expected from Finnish cancer registry data for 1980, but the breast cancer mortality was lower than expected (a rate ratio of 0.75). The latter difference occurred mainly in Years 3-6 of the follow-up period. The effect seemed similar in women under and over the age of 50 years. The cohort was of higher educational status than the Finnish population, and the mortality from all causes was lower than the general Finnish population, an effect seen in previous studies of compliers with breast screening.

The reduction in mortality from breast cancer in the study cohort is consistent with an effect of the BSE-containing Mama program, though selection bias, inherent in any observational study of screening, provided an alternative explanation for the findings.