[Observed effects of the mass screening program for breast cancer in Nijmegen in 1975-1986].

Since January 1975, the start of the screening programme for breast cancer in the city of Nijmegen, The Netherlands, over 14 years have elapsed. Data up to the end of 1986 have been processed and are presented in this article. The younger the birth cohort, the higher the attendance rate. In the course of the screening programme, attendance rates decline. Referral rates are highest in the first screening round and for the eldest birth cohort. Detection rates increased during the most recent screening rounds, after an initial decrease during the earliest rounds. They are higher for the eldest birth cohort also. The relative number of interval carcinomas is highest among younger women (as related to the screening-detected carcinomas).