Incidence of thyroid cancer in Norway 1970-1985. Population review on time trend, sex, age, histological type and tumour stage in 2625 cases.

In the Norwegian population, a total of 1977 females and 648 males had a diagnosis of thyroid cancer and were reported to the Cancer Registry during 1970-85. Most of the cases (98%) were histologically or cytologically confirmed, and 141 cases were diagnosed at autopsy (5.4%). Of the patients with information available, 13% had not been subjected to radical surgery. The actual number and annual incidence rate of thyroid cancer increased during the period, especially among females, although a possible levelling off was observed at the end. The frequency of papillary carcinoma clearly increased with time, and tumours were more often localized at presentation in later years. Improved detection of smaller tumours and differences in histopathological judgement may in part explain these results, but our findings are so notable that etiological factors must also be accounted for and researched. Associations between sex, age, histology and stage were further studied in a multivariate log-linear model. The results confirm the importance of sex and age when exploring the observed incidence pattern and also show that various histological types are unique with respect to metastatic patterns, when confounding factors have been adjusted for.