Diagnosis of metastatic tumours to the thyroid gland by fine needle aspiration biopsy

Introduction: Malignant metastases are rarely found in the thyroid gland, the incidence reaching approximately 2% of all thyroid malignant neoplasms. They are most often caused by tumours of the kidneys, lungs, mammary glands, ovary, and colon or by melanomas. The aim of the study was to evaluate the usefulness of fine needle aspiration biopsy (FNA) for diagnosing tumour metastases to thyroid glands. Material and methods: A total of 15122 patients were operated between 1990 and 2009 for goitres. Malignant neoplasm was diagnosed in 733 (4.8%) patients. Malignant metastases to the thyroid gland were detected in 10 patients, namely 2 men and 8 women aged 48-89 years. The group made up 1.4% of all patients operated for malignant thyroid tumour. Preoperative diagnostic procedure consisted of thyroid scintigraphy, thyroid ultrasonography, and cytology of the material obtained through FNA. In addition, the hormonal activity of the thyroid gland was examined. The range of operation was established through clinical assessment of the tumour, preoperative cytology, and intra-operative histopathology. Results: Among 7 patients with thyroid metastases from renal clear cell carcinoma, as diagnosed postoperatively, cytology of the thyroid material obtained through FNA revealed follicular tumour in 3 (43%) patients, tumour cells in 2 (28.5%) and atypical cells in the other 2 (28.5%). Intraoperative histopathology confirmed the presence of metastasis from renal clear cell carcinoma (1) and indicated thyroid medullary cancer (1), follicular tumour (4), or trabecular adenoma with necrosis (1). Among two patients with thyroid metastases from breast cancer, cytology confirmed a metastasis from breast cancer in one (the woman was disqualified for surgical treatment) and indicated follicular tumour in one. Intraoperative histopathology suggested thyroid anaplastic cancer. Examination of biopsy specimen revealed epithelial cells accompanied by cell atypia in one patient with thyroid metastasis from lung cancer. Intra-operative examination also indicated cellular atypia in the same patient. Conclusions: Follicular tumour diagnosed by fine needle aspiration biopsy in patients after treatment for other cancers, especially renal clear cell carcinoma, should alert the surgeon to the possibility that it could be a metastasis of this cancer to the thyroid gland. (Pol J Endocrinol 2010; 61 (5): 427-429)