Geographic pathology of occult thyroid carcinomas.

Thyroid glands obtained from patients in southeastern Canada, northeastern Japan, southern Poland, western Colombia, and from Japanese living in Hawaii were serially step-sectioned and examined microscopically using identical techniques and diagnostic criteria. The prevalence of occult papillary thyroid carcinoma was significantly higher in Japan (28.4%) and in Hawaiian Japanese (24.2%) when compared with Canada (6%), Poland (9.1%), and Colombia (5.6%). The carcinomas were all papillary except for a single follicular lesion from Colombia. There was no significant sex prevalence. Most of the patients were between 40 and 79 years of age, but there was no particular predominant decade. Only the Colombian series had a large number of younger patients, and they showed a slightly lower prevalence of occult carcinomas before age 40. Most papillary thyroid carcinomas grow slowly and probably remain occult for the life of the patient.