Metastatic melanoma mimicking an angiomatoid fibrous histiocytoma

Abstract

Melanoma is known for its remarkable histopathological heterogeneity, capable of mimicking both epithelial and mesenchymal neoplasms. We report the case of a 46-year-old male who was externally diagnosed with sarcoma and presented with a subcutaneous pre-sternal mass comprising a proliferation of epithelioid–histiocytoid cells, hemosiderin deposition, and chronic inflammation, closely resembling an angiomatoid fibrous histiocytoma (AFH). A peripheral pseudo-capsule and a pericapsular lymphocytic cuff were also observed. Immunohistochemically, the tumour cells were focally positive for desmin and S100 protein, but negative for EMA, CD99 and CD68. Further studies demonstrated SOX10 positivity and identified a BRAF p.V600E mutation, findings consistent with melanoma. Review of the external clinical history confirmed that the patient had undergone surgery for a melanoma near the current lesion site three years earlier. In conclusion, the integration of histology, immunohistochemistry, molecular studies and clinical history is essential for the accurate diagnosis of melanoma and for avoiding misdiagnosis.