Background: 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 a terminal event, and the effectiveness of conventional treatment has been questioned. The authors assessed the effects of current methods of diagnosis and treatment on the course of the disease.
Methods: Forty-three patients with metastasis to the thyroid gland were studied retrospectively. Primary tumor origin was identified in all but two cases. Metastasis to the thyroid gland was confirmed by fine-needle aspiration cytology or histology. Data were analyzed for the frequency and types of malignant lesions, the clinical course of disease, and the prognosis after thyroid involvement.
Results: The kidney was the most common primary tumor site (33%), followed by lung (16%), breast (16%), esophagus (9%), and uterus (7%). The time from diagnosis of the primary tumor to metastasis to the thyroid gland was considerable for renal cell adenocarcinoma (mean, 106 months) and for adenocarcinomas of the breast (mean, 131 months) and uterus (mean, 132 months). In 12 patients, this interval was more than 120 months. Fine-needle aspiration cytology detected metastatic malignancy in 29 of 30 patients. Treatment involved surgery alone, surgery with adjuvant therapy, or nonsurgical methods. Two patients with uterine adenocarcinoma and one with breast adenocarcinoma had disease regression with no evidence of tumor recurrence.
Conclusions: In any patient with a previous history of malignancy, no matter how remote that history is, a new thyroid mass should be considered recurrent malignancy 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.