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, and increases in the incidence have been observed worldwide. We investigated temporal trends in breast cancer incidence in the southeastern Netherlands between 1960 and 1989 by birth cohort analysis, using data of the Eindhoven Cancer Registry. An overall time-trend in incidence rate was estimated, based on age and year of diagnosis. Rate ratios were calculated, as the ratio of the observed versus the expected incidence rates, which was based on the estimated time-trend. In this unscreened population the age-specific incidence increased for every successive birth cohort in the period 1880-1949. Women born between 1940 and 1949 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 expected 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 this changing trend.