Age-period-cohort analysis of cervical cancer incidence in Taiwan: Differences between squamous cell carcinoma and adenocarcinoma

To examine the etiologic distinction between squamous cell carcinoma and adenocarcinoma of the cervix, the relationship between the incidence of both histotypes of cancer and age at diagnosis, time period at diagnosis and birth cohort was analyzed using data from the Taiwan Cancer Registry. Included in the study were all cases of both histotypes occurring during the period 1979-90 within a population of Taiwanese women aged 25 to 75 years. A log-linear model modified from the method of Osmond and Gardner was used for the analyses. Age-period-cohort analyses of age effect indicated that, prior to the age group of 49-51, there is an almost identical incidence of both histotypes with an approximate linear trend of age effect but that, after this time, there is a divergence, with the age effect of increase slightly declining with age for squamous cell carcinoma and clearly declining for adenocarcinoma. In regard to period and cohort effects, a substantial moderation of squamous cell carcinoma risk was exhibited with both advancing recent calendar periods and birth cohorts, while adenocarcinoma risk also has a moderation but to a lesser extent. The model also identified the changes in female sex hormones after the menopause as a determinant of the differing age effects, the efficiency of Pap smear screening practices as a determinant of the differing period effects, and changes in reproductive patterns as a determinant of the differing cohort effects. These findings may provide clues with which to develop etiologic hypotheses and support the contention of etiologic distinctions between both histologic types.