Primary cutaneous myxoid melanoma: immunohistologic clues to a difficult diagnosis.

We describe a 25-year-old man with a primary cutaneous myxoid malignant melanoma and xeroderma pigmentosum. Histologically, the tumor had a lentiginous intraepidermal component and a dermal myxoid nodule containing fusiform cells with hyperchromatic nuclei and nuclear pseudoinclusions. Immunohistochemically, the tumor cells were positive for S-100 protein in both the epidermis and the dermis and did not stain with HMB-45, AE1-AE3, MNF 116, antiactin, or anti-p53 protein. Although this tumor is rare, it should be considered in the differential diagnosis of cutaneous myxoid lesions.