PAROTID INVOLVEMENT BY DESMOPLASTIC MELANOMA

Desmoplastic malignant melanoma often arises in sun damaged skin of th e head and neck and shows frequent neurotropism, Although metastatic m elanoma frequently involves the parotid, direct spread to the parotid has been rarely reported, We evaluated five cases of desmoplastic mali gnant melanoma involving the parotid gland with clinical and pathologi cal evidence of precursor cutaneous lesions in four of the five cases, The parotid involvement in four cases was tumoural, and three of thes e were not clinically suspected to be melanoma. The histological appea rance in all five cases was that of a sarcomatoid tumour, Immunohistoc hemistry and electronmicroscopy performed on three of the cases showed only evidence of schwannian differentiation: the tumour cells were po sitive for S-100 protein and vimentin, and negative for cytokeratin an d HM8-45, Electronmicroscopy showed no evidence of melanogenesis. All live tumours showed histological evidence of prominent neurotropism wi th one case demonstrating extension from overlying skin along cutaneou s nerves to the superficial parotid, Thus, desmoplastic malignant mela noma may involve the parotid by neurotropic spread and can be patholog ically indistinguishable from malignant schwannoma, a diagnosis which may be made erroneously in the absence of clinical information.