Metastasis to the thyroid gland; unusual site of metastasis

The incidence of metastasis to the thyroid gland in autopsy series varies from 1.25 % to 24%. Metastasis to the thyroid gland is usually considered as a terminal event, and the effectiveness of conventional treatment has been questioned.

Seven patients with metastasis to the thyroid gland were studied retrospectively. Primary tumor origin was identified in all of them. Metastasis to the thyroid gland was confirmed by fine needle aspiration cytology or histology. Data were analyzed for the type of malignant lesions, the clinical course of the disease, and the prognosis after thyroid involvement.

Two patients had lung as a primary tumor site. Breast, iris, kidney, parotid and soft tissue sarcoma were the involved primary sites in the other cases. The time from the diagnosis of primary tumor to metastasis to the thyroid gland was considerable (ranged from 13- 135 months, median 60 months). Fine needle aspiration cytology detected metastasis in five of seven patients. Treatment was surgery alone or surgery with adjuvant therapy. One patient didn't receive any treatment.

In any patient with a previous history of malignancy, no matter how old that history is, a new thyroid mass should be considered as recurrence until proved otherwise. Although detection of metastasis to the thyroid gland often indicates poor prognosis, aggressive surgical and medical therapy may be effective in a small percentage of patients.