Diagnostic lessons of mucosal melanoma with osteocartilaginous differentiation

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Abstract
Aims: To document the clinical, morphological and immunohistochemical features of two cases of primary mucosal melanoma with osteocartilaginous differentiation. Materials and methods Two cases of mucosal melanoma with cartilage and bone formation are reported, one arising in the vagina of a 79‐year‐old woman and one in the oral cavity of a 67‐year‐old man. The vaginal melanoma exhibited only cartilaginous differentiation. The oral cavity mucosal melanoma exhibited both bone and cartilage formation and was remarkable for its multifocality, long history not associated with metastases and its lengthy manifestation of dual morphologies: some of the tumours were typical in situ/invasive melanotic melanomas whilst the others were composed of amelanotic spindle and epithelioid cells with osteocartilaginous tissue. One of the lesions exhibited in situ and invasive melanoma with transition to an osteogenic tumour in places. The patient also developed non‐osteogenic malignant melanomas in the nasal cavity and nasopharynx. Conclusions Malignant melanomas showing foci of osteocartilaginous differentiation are extremely rare with only 18 cases reported. Primary mucosal malignant melanomas of vagina and oral cavity showing osteocartilaginous differentiation have not previously been documented. Primary vaginal melanoma with cartilaginous differentiation must be distinguished from primary malignant mixed Müllerian tumour whilst malignant change in a pleomorphic adenoma, sarcomatoid carcinoma, osteogenic sarcoma and mesenchymal chondrosarcoma are included in the differential diagnosis of primary oral mucosal melanomas with osteocartilaginous differentiation. In this context, immunohistochemistry using antibodies to cytokeratin, S100 protein and MIC2 is of value.