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.

Breast cancer in the southeastern Netherlands, 1960-1989: trends in incidence and mortality.

Temporal trends in incidence and mortality in breast cancer were examined in the southeastern Netherlands using data from the population-based Eindhoven Cancer Registry. In the period 1960-1989 the incidence rate of first primary breast cancer approximately doubled in all age groups. The increase mainly occurred before 1975 and after 1985, when no screening activities were performed. This trend appeared to be a result of an average yearly increase in incidence of localised and distant tumours with both 4.6%, whereas the incidence of regional tumours did not change. Simultaneously, breast cancer mortality remained unchanged in women aged under 60, and only increased by a yearly average of 0.7% in women aged 60-74 and of 0.9% in women aged 75 and over. These differing trends in incidence and mortality, which can only partially be explained by earlier detection, suggest an improved survival of breast cancer.