Value of aspiration cytology of the thyroid in metastatic disease.

Metastases may simulate primary malignant tumors of the thyroid, causing problems in the diagnosis and management of patients with a history of cancer. In the seven-year period of July 1978 through June 1985, 8 of 549 needle aspirates of the thyroid contained metastatic tumor, 6 of which were subsequently confirmed by histologic study. The primary sites of origin were the breast, kidney, colon and stomach as well as lymphoma. The cytologic features observed in the aspiration biopsy material from the six cases were characteristic of each of the primary tumors. Three of the patients had had prior resections of carcinomas (breast, colon and stomach) while in three patients the cytologic diagnosis of the thyroid aspirates led to the discovery of the primary tumor (kidney and two lymphomas). One case of lymphoma/leukemia and one case of previously biopsied lung carcinoma were confirmed on clinical grounds. It is of critical importance that primary thyroid neoplasms occurring in patients known to have primary tumors elsewhere be distinguished from disseminated tumors involving the thyroid. Our experience suggests that fine needle aspiration is of considerable value in this differential diagnosis. Needle aspirates of the thyroid are also of value in leading to the diagnosis of unsuspected nonthyroidal primary cancer.