Incidence of thyroid cancer in Japan.

The incidence of thyroid cancer was analyzed based on data provided by cancer registration in Japan and also based on data for 11,104 cases of thyroid cancer registered at the Japanese Committee for Registration of Malignant Neoplasm of Thyroid (JCR-MNT) from 1977 through 1986. Incidence rates for men and women gradually increased over the study period from 1959 through 1985. The age-adjusted rates for 1985 showed 1.1 per 100,000 for men and 3.1 per 100,000 for women. The higher rates were observed in Hiroshima and Nagasaki cities. Male to female ratio was 1:6 in papillary and follicular carcinomas and 1:2 in medullary and anaplastic carcinomas. Papillary, follicular, and medullary carcinomas are more common in the fifth and sixth decades of life while anaplastic carcinoma is more common in the elderly. The age-specific rates by histological classification showed no change over the study period of 1977 through 1986. The increased incidence could be attributed to improvements in diagnostic procedures.