EFFICACY OF MAMMOGRAPHIC SCREENING OF THE ELDERLY - A CASE-REFERENT STUDY IN THE NIJMEGEN PROGRAM IN THE NETHERLANDS

Background: Only a few small studies have been conducted to examine th e usefulness of mammographic screening in elderly women. These studies suggest that the screening-related reduction in breast cancer mortali ty rates is less than the estimated 20%-40% reduction observed for wom en aged 50-70 years at the time of their first screening. Purpose: We have studied the efficacy of continued mammographic screening for brea st cancer of elderly women within our screening program. Methods: In 1 975, a breast cancer screening program was started in the city of Nijm egen, The Netherlands. During each biennial screening round, approxima tely 30 000 women aged 40 years and older were personally in invited t o participate. Single-view mammography was administered. The present s tudy was conducted using a case-referent design. In order to be eligib le for inclusion in this study, women had to have been invited to part icipate 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 die d of breast cancer at some point during 1977 through 1988. Referents w ere matched for age at last invitation to screening prior to the diagn osis of breast cancer and for the number of previous invitations to sc reenings. Five referents were randomly selected for each case. Breast cancer mortality rate ratios (RR) were calculated for several categori es of attendance to the screening. Results: The RR of those who attend ed the last screening versus those who failed to do so was 0.58 (95% c onfidence 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 a fter the age of 65, relative to those who attended before 65 only, was 0.26 (95% CI 0.05-1.32). Conclusion: Although self-selection bias was present in our data, it was not likely to be responsible for the bene ficial effect in women aged 65-74 at the time of invitation to screeni ngs. It probably was responsible for the reversed RR (RR > 1) in the g roup of women 75 gears and older. Implication: Continuation of mammogr aphic screening until at least the age of 75 years may lead to a reduc tion of breast cancer mortality among elderly women.