Efficacy of Mammographic Screening of the Elderly: a Case-Referent Study in the Nijmegen Program in The Netherlands

Abstract

Only a few small studies have been conducted to examine the usefulness of mammographic screening in elderly women. These studies suggest that the screening-related reduction in breast cancer mortality rates is less than the estimated 20%-40% reduction observed for women aged 50-70 years at the time of their first screening. We have studied the efficacy of continued mammographic screening for breast cancer of elderly women within our screening program. In 1975, a breast cancer screening program was started in the city of Nijmegen. The Netherlands. During each biennial screening round, approximately 30,000 women aged 40 years and older were personally invited to participate. Single-view mammography was administered. The present study was conducted using a case-referent design. In order to be eligible for inclusion in this study, women had to have been invited to participate in the mammography screening program at least twice, with the most recent invitation having occurred when each woman was 65 years or older. The cases studied comprised 33 women in this group who had died of breast cancer at some point during 1977 through 1988. Referents were matched for age at last invitation to screening prior to the diagnosis of breast cancer and for the number of previous invitations to screenings. Five referents were randomly selected for each case. Breast cancer mortality rate ratios (RR) were calculated for several categories of attendance to the screening. The RR of those who attended the last screening versus those who failed to do so was 0.58 (95% confidence interval [CI] = 0.24-1.41); for women aged 65-74, the RR was 0.34 (95% CI = 0.12-0.97) and for women aged 75 or over, 2.87 (95% CI = 0.62-13.2). The RR of those who attended the screening before and after the age of 65, relative to those who attended before 65 only, was 0.26 (95% CI = 0.05-1.32). Although self-selection bias was present in our data, it was not likely to be responsible for the beneficial effect in women aged 65-74 at the time of invitation to screenings. It probably was responsible for the reversed RR (RR > 1) in the group of women 75 years and older. Continuation of mammographic screening until at least the age of 75 years may lead to a reduction of breast cancer mortality among elderly women.