Ovarian cancer histology-specific incidence trends in Canada 1969-1993: age-period-cohort analyses.

This study examined histology-specific incidence trends of ovarian cancer in Canada, 1969-1993. The impact of age, period and cohort effects on these trends were studied by means of age-period-cohort analysis. Age-standardized incidence rates of serous, endometrioid, clear cell and germ cell tumours increased significantly and the rates of sex cord-stromal and other classified epithelial ovarian tumours decreased considerably. The rates of mucinous and NOS/unclassified tumours remained unchanged. Cohort effect has a major impact on incidence trends of serous, endometrioid, germ cell, sex cord-stromal and other classified epithelial ovarian tumours but no meaningful impact on trends of mucinous, clear cell, or NOS/unclassified ovarian tumours. Various cohort patterns by histology subtypes were observed: the risk of developing serious tumours increased markedly among birth cohorts of 1895-1930, stabilized thereafter and decreased among young cohorts of 1950-1960; the risk of germ cell tumours increased significantly among young cohorts of 1965-1980; and the risk of sex cord-stromal tumours dropped constantly among cohorts 1910-1950. Various period patterns by histology subtypes observed in this study suggested changes in histology classification criteria over the period. Further studies need to consider the various etiologies and the classification criteria changes according to histology subtypes.