Mammographic screening after the age of 65 years: evidence for a reduction in breast cancer mortality.

We evaluated whether regular mammographic screening of women aged 65 years or older affected breast cancer mortality. In Nijmegen, a population-based screening program for breast cancer was started in 1975, with biennial mammography for women aged 35-64 years. Since 1977, elderly women have also been participating. For the present case-control study, women were selected who were over 64 years of age at the most recent invitation. Eighty-two of them had died from breast cancer. For these cases, 410 age-matched population controls were selected. The ratio of breast cancer mortality rates of the women who had participated regularly (ie., in the 2 most recent screening rounds prior to diagnosis) vs. the women who had not participated in the screening was 0.56 (95% CI = 0.28-1.13). The rate ratio was 0.45 in the women aged 65-74 years at the most recent invitation (95% CI = 0.20-1.02), whereas it was 1.05 in the women aged 75 years and older (95% CI = 0.27- 4.14). While the breast cancer survival rate of the non-participant patients was fairly equal to that of patients from a control population, the underlying incidence rate of breast cancer was higher in the participants than in the non-participants. Therefore, we conclude that bias was present, but that it had decreased our effect estimate. The real reduction in breast cancer mortality due to regular screening will be even larger. Regular mammographic screening of women over age 65 (at least up to 75 years) can reduce breast cancer mortality by approximately 45%.