Diagnostic dilemma: late presentation of amelanotic BRAF-negative metastatic malignant melanoma resembling clear cell sarcoma: a case report.

UNLABELLED: Clear cell sarcoma is a rare cancer primarily of tendons, fascia, and aponeuroses that can be difficult to discern from primary cutaneous malignant melanoma. The two cancers share several histological markers, with most cases of both cancers staining positively for S-100, HMB-45, and melanin. Primary therapy of both cancers involves wide local excision, but while systemic therapy has proven benefit for malignant melanoma, it has not been established for clear cell sarcoma.We report the case of a 58 year old woman with a large, ulcerated, fungating mass on her left lower leg. Frozen section of the mass showed a malignant epithelioid and spindle cell tumor confined to the subcutaneous tissue. A provisional diagnosis of soft-tissue sarcoma was made. Through in-depth study of initial biopsy with immunohistochemistry for S-100, HMB-45, MART-1, and MITF, along with karyotyping and FISH analysis for EWS gene rearrangement, the diagnosis of amelanotic malignant melanoma was confirmed. The patient then underwent systemic treatment with ipilimumab upon recurrence with good response.

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