IS THE PEAK IN BREAST-CANCER INCIDENCE IN SIGHT - A STUDY CONDUCTED IN THE SOUTHEASTERN NETHERLANDS

Breast cancer is the most frequent malignancy in the western world, an d increases in the incidence have been observed worldwide. We investig ated temporal trends in breast cancer incidence in the southeastern Ne therlands between 1960 and 1989 by birth cohort analysis, using data o f the Eindhoven Cancer Registry. An overall time-trend in incidence ra te was estimated, based on age and year of diagnosis. Rate ratios were calculated, as the ratio of the observed versus the expected incidenc e rates, which was based on the estimated time-trend. In this unscreen ed population the age-specific incidence increased for every successiv e birth cohort in the period 1880-1949. Women born between 1940 and 19 49 had the highest age-specific incidence rates with an excess of 10% (relative risk 1.10, 95% confidence interval 1.01-1.22). The incidence rates in women born after 1949 declined and were 21% lower than expec ted by the estimated secular trend (relative risk 0.79, 95% confidence interval 0.64-0.96). This decrease in incidence for women aged under 40 suggests that the peak in incidence of female breast cancer may be in sight. It remains unclear which risk factors are responsible for th is changing trend. Key words: breast cancer, cancer registry, incidenc e, birth cohort