Metastatic merkel cell carcinoma to the thyroid gland: Case report and review of the literature

Background: Merkel cell carcinoma (MCC) is an aggressive and rare neuroendocrine tumor, accounting for less than 1% of skin cancers. Metastasis primarily manifests in the cervical lymph nodes but rarely affect the thyroid. Methods: We report a case of primary head and neck cutaneous MCC with metastasis to the thyroid gland. A review of the literature of MCC with thyroid metastasis was conducted. Results: We identified five cases of MCC with thyroid metastasis. Primary sites included the distal upper and lower extremities, axilla, buttock, and groin. Treatment courses varied including thyroidectomy, immunotherapy, and expectant palliative measures. Time from initial diagnosis to thyroid metastasis ranged from four months to four years. Tissue diagnosis was achieved in 5 of 6 cases. Conclusions: MCC with thyroid metastasis is rare and likely represents aggressive disease. Despite advances in treatment and surveillance, outcomes for MCC remain poor. Ongoing research may establish predictors for treatment response.