DIAGNOSTIC LESSONS OF MUCOSAL MELANOMA WITH OSTEOCARTILAGINOUS DIFFERENTIATION

Aims: To document the clinical, morphological and immunohistochemical features of two cases of primary mucosal melanoma with osteocartilagin ous differentiation. Materials ann methods: Two cases of mucosal melan oma 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 differenti ation. The oral cavity mucosal melanoma exhibited both bone and cartil age formation and was remarkable for its multifocality, long history n ot associated with metastases and its lengthy manifestation of dual mo rphologies: some of the tumours were typical in situ/invasive melanoti c melanomas whilst the others were composed of amelanotic spindle and epithelioid cells with osteocartilaginous tissue, One of the lesions e xhibited in situ and invasive melanoma with transition to an osteogeni c tumour in places, The patient also developed nonosteogenic malignant melanomas in the nasal cavity and nasopharynx. Conclusions: Malignant melanomas showing foci of osteocartilaginous differentiation are extr emely rare with only 18 cases reported. Primary mucosal malignant mela nomas of vagina and oral cavity showing osteocartilaginous differentia tion have not previously been documented, Primary vaginal melanoma wit h cartilaginous differentiation must be distinguished from primary mal ignant mixed Mullerian tumour whilst malignant change in a pleomorphic adenoma, sarcomatoid carcinoma, osteogenic sarcoma and mesenchymal ch ondrosarcoma are included in the differential diagnosis of primary ora l mucosal melanomas with osteocartilaginous differentiation. In this c ontext, immunohistochemistry using antibodies to cytokeratin, S100 pro tein and MIC2 is of value.