EPIDEMIOLOGIC STUDIES ON THYROID CANCER IN NAGANO PREFECTURE, JAPAN

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Abstract
During 1965 to 1966, thyroid cancer combined with goiter was surveyed in an unselected population living in 9 non-goitrous areas in Nagano Prefecture, Japan. In the survey, 30,359 subjects were examined. The total number of goiter patients found in the population was 1,228; i.e. 4.0% (1.7 males; 6.1 females) of the population examined. The 353 cases of the 1,228 patients were clinically diagnosed as nodular goiter, in which 234 cases had indications of surgical removal of thyroid nodules, and 186 of the 234 cases were operated on. In the clinical and histological studies, 40 cases (11 males; 29 females) were diagnosed as thyroid cancer. The prevalence rate of thyroid cancer was 1.3 (0.8 males; 1.8 females) per 1,000 subjects examined, and was not the same in different areas and was higher in the age-group over 30 than in the age-group under 29. About 20% of the nodular goiters which were operated on were thyroid cancer and 15.9% which was clinically diagnosed as benign nodular goiter before operation were thyroid cancer. Most of patients with thyroid cancer were unaware of the presence of goiter and showed no symptom. About 1/3 of thyroid cancer were in advanced stadium clinically, and 2 of them were too advanced to be operated on. The 38 cases which were operated on were histologically diagnosed as papillary adenocarcinoma, with the exception of 2 cases of follicular adenocarcinoma. There is a distinct difference between the prevalence rate of thyroid cancer and the mortality or morbidity (incidence) rate of thyroid cancer, and the former is significantly higher than the latter.

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