Melanotic medullary thyroid carcinoma: A case report with review of the literature

Melanotic medullary thyroid carcinoma is morphologically defined by the presence of melanin deposits in the cytoplasm of tumor cells. It is an extremely rare variant with only 15 cases described in the literature to date and only one report of diagnosis by fine needle aspiration (FNA) biopsy. A 51-year-old woman presented with neck swelling. An ultrasound examination revealed a single solid nodule in the right thyroid lobe that measured 5.4 × 4.7 × 4.3 cm. Laboratory examination revealed elevated levels of serum calcitonin (8643.0 pg/ml), carcinoembryonic antigen (CEA) (86.2 ng/ml), and chromogranin A (123.2 ng/ml). An FNA biopsy of the thyroid nodule revealed predominantly single plasmacytoid cells with round to oval eccentric nuclei and dark brown intracytoplasmic granules. Immunohistochemical studies with Melan-A performed on a cell block slide confirmed that the granules contained melanin. The tumor cells were also positive for calcitonin, CEA, synaptophysin, AE1/AE3, CAM5.2, and HMB-45(focal); the tumor cells were negative for chromogranin, thyroglobulin, PAX8 and TTF-1. The diagnosis was reported as melanotic variant of medullary thyroid carcinoma. The patient underwent a total thyroidectomy which revealed tumor cell expression of insulinoma-associated protein 1 and confirmed neuroendocrine differentiation. Shortly after she presented with tumor recurrence in the thyroidectomy bed. The tumor cells were positive for only S100, SOX10, and Melan-A. Molecular analysis with the SEMA4 Solid Tumor Panel revealed mutations in the HRAS, PIK3CA, PIK3R1, MYC, and CCND3 genes. The final diagnosis was reported as melanocytic medullary thyroid carcinoma with high grade transformation and loss of epithelial and neuroendocrine expression.