Incidence of sporadic and familial medullary thyroid carcinoma in Sweden 1959 through 1981. A nationwide study in 126 patients. Swedish MCT Study Group.

Medullary thyroid carcinoma (MTC) was identified in 276 patients (in 27 diagnosed at autopsy) by a review of virtually all 6,513 notifications of primary thyroid cancer ot the National Cancer Registry in Sweden 1959 through 1981. The diagnosis was confirmed in 268 of the 276 cases by histopathological and histochemical reexamination. Anamnestic data and morphological characteristics indicated that 208 (75%) patients had sporadic and 68 (25%) familial MTC. The mean ages at diagnosis of these two groups were 57.0 and 42.6 years respectively. The age-standardized incidence rate per 10(5) inhabitants was 0.18 for males and 0.23 for females. The age-specific incidence of sporadic MTC increased markedly with age, whereas no unequivocal rise was found after the age of 20 for familial disease. Standardized morbidity ratios (SMR), calculated separately for each of the six Swedish health care regions, revealed a roughly two-fold and mostly non-significant geographical variation in the occurrence of sporadic MTC. SMR for familial disease varied, however, between 0 and 306 and deviated highly significantly from the national average in four of the six regions. Regional differences in diagnostic intensity were considered unlikely as the sole explanation of this finding.