Metastasis of Merkel Cell Carcinoma to the Thyroid Gland: a Case Report

Merkel cell carcinoma (MCC) is an uncommon neuroendocrine cutaneous malignancy. The thyroid gland is an exceptionally rare site of metastasis for MCC. Thus, metastasis to the thyroid gland may entail diagnostic difficulties. An 82-year-old man presented with a palpable neck tumor in the right anterior neck. Computed tomography scan revealed a 3.4 cm, enhancing tumor in the right thyroid gland. The patient underwent fine needle aspiration, and cytologic and immunohistochemical findings revealed metastasis of MCC to thyroid gland. We decided to perform surgical excision of the right thyroid gland. The patient was discharged 2 days after surgery without any complications. Various immunohistochemical studies were performed with the surgical specimen. The tumor cells were positive for CK 20 and CD 56, but negative for thyroid transcription factor-1. Finally, the histopathologic diagnosis confirmed as metastasis of MCC to the thyroid gland. Here, we present an exceedingly rare metastasis of MCC to the thyroid gland and discuss its diagnosis and treatment. In patients with a known history of a primary malignancy, the differential diagnosis of any abnormal findings in the thyroid gland should always include possibility of potential metastasis.