Thyroid cancer in Connecticut, 1935-1975: an analysis by cell type.

Incidence data from the Connecticut Tumor Registry for the years 1935-1975 were examined for changing patterns in the rates of thyroid cancer and its four major cell types. Both males and females exhibited a 5-fold increase in age-adjusted thyroid cancer rates over the 41 years, with a nearly constant female:male ratio of 3:1. Papillary and follicular carcinomas were the cell types responsible for the upward trend. Birth cohort analysis revealed cohort effects, especially for females with papillary carcinoma. Age-specific incidence curves for the cohorts born after 1910 showed progressive increases in slope until the 1960 cohort, when the slope decreased. This pattern coincides with the widespread use of radiation therapy for benign conditions of the head and neck among children and adolescents from the early 1920s to the late 1950s. Fitting a logistic model to these data produced relative risks for successive birth cohorts which were consistent with the effects of radiation exposure.