Abstract

Introduction: Malignant melanoma can occasionally adopt an epithelioid and rhabdoid morphology which can often make diagnosis challenging. While some genetic mutations can confer an epithelioid morphology such as beta-catenin and PRKAR1, these are typically associated with certain melanocytic tumors, such as deep penetrating nevi and pigmented epithelioid melanocytoma. Herein, we present a case of a very aggressive epithelioid and rhabdoid appearing melanoma demonstrating loss of INI-1, which can be seen in non-melanocytic tumors such as epithelioid sarcoma. Case: A 39-year-old woman presented with a palpable mass in the right axilla, which was determined to be melanoma by fine needle aspirate. She was found to have disease in two of sixteen lymph nodes. Surgical excision showed four subcutaneous in-transit metastases with no additional involved lymph nodes. Histologic sections showed a proliferation of markedly atypical melanocytes with vesicular chromatin with prominent eosinophilc nucleoli, and scant pigmentation. Scattered epithelioid and rhabdoid cells were present, and the rhabdoid cells showed eccentric nuclei, prominent nucleoli, and hyaline cytoplasmic inclusions. The malignant cells were positive for melanocytic markers, including HMB45, S100, and Melan-A, by immunohistochemistry. INI-1 was lost in the tumor cells with positive internal control. The patient’s melanoma was aggressive despite treatment and she developed lung metastases three months after initial diagnosis and died seven months later. Conclusion: In this study, we show a case of melanoma with epithelioid and rhabdoid morphology that showed loss of INI-1 and an aggressive clinical course. This case highlights that some melanomas can show loss of INI-1 and could represent a potential pitfall and misclassification. Furthermore, this case suggests that melanoma with loss of INI-1 could be associated with a worse prognosis, though additional studies are needed in this regard.

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