Meatastatic melanoma to the thyroid gland

Melanoma metastásico a glándula tiroides

Introduction: metastases to the thyroid gland are a rare finding. They occur more frequently in women and may be synchronous or metachronous, by dissemination from distant organs or by direct extension. Their appearance is associated with a poor prognosis and low survival rate. The metastasis rate to this gland by malignant melanoma is 1%, so the approach by cytology is limited, as it shares characteristics with papillary thyroid carcinoma. Case report: a 50-year-old woman, in follow-up for a nodular invasive malignant melanoma in the right frontotemporal region. During follow-up visits, a CT of the neck showed reactive cervical lymph nodes, and an ultrasound revealed a left thyroid lobe nodule that had increased its volume 100% in three months. Discussion: fine needle aspiration revealed epithelial cell papillary formations, irregular nuclei, some exhibiting nuclear inclusions and clefts, being classified as Bethesda VI. A left hemithyroidectomy was performed observing a 1.8 x 1.6 cm whitish mass with irregular margins.  Histological analysis showed epithelioid cells, with pleomorphic nuclei and prominent nucleoli. Immunolabeling was positive for SOX-10, S100, HMB45, melan-A and galectin-3 and negative for AE1/AE3, TTF1, thyroglobulin, PAX8 and calcitonin. It was determined that the lesion corresponded to a metastatic melanoma to the thyroid gland.   Conclusions: metastases to the thyroid gland are rare but considering melanoma is regarded as one of the simulating neoplasms, it becomes a diagnostic challenge.