Occult micropapillary carcinoma associated with benign follicular thyroid disease and unrelated thyroid neoplasms.

Surgically resected thyroids from 425 patients with thyroid disease other than carcinoma of follicular cell derivation were thoroughly examined for occult micropapillary carcinoma (MPC). There were 317 cases of nodular hyperplasia, 36 of thyroiditis, 44 follicular adenomas, and 28 others. Glands were sectioned at 2- to 3-mm intervals and fixed in formalin. Every section was examined histologically. There were 71 cases (16.7%) of MPC containing 118 tumors. Among 343 women, 51 (14.9%) had MPC; among 82 men, 20 (24.4%) had MPC. The average age of all of the patients was 46.9 years and of those with MPC, 50.5 years. The occurrence of MPC peaked between 40 and 70 years and declined in older patients. MPC was found in 8.9% of patients who underwent lobectomies, 10.8% who had hemithyroidectomies, and 24.1% of those who had total thyroidectomies. Logistic regression analysis revealed significant associations between the presence of MPC and the patient sex, age, and extent of surgery; in contrast, there was no association between the occurrence of MPC and the underlying thyroid disease. These data indicate that MPC is present in up to 24.1% of thyroids removed for unrelated thyroid disease. The predominance of this lesion in men is in striking contrast to the occurrence of clinically significant thyroid cancer. This suggests that the initiation of carcinogenesis is not sexually dimorphic, whereas promoters of tumor growth are. A rational management of this common disease awaits the results of careful controlled trials.