Primary chondroid melanoma

Background: Malignant melanoma is notorious for the wide range of histologi c patterns it can assume, among the least frequent of which is chondroid me lamona. Methods: Two cases of primary chondroid melanoma of the distal lower extrem ity were studied. Tissue for light microscopy was fixed in formalin, embedd ed in paraffin, and processed routinely. In one case, transmission electron microscopy and immunohistochemical evaluation were performed. Results: Both cases exhibited melanoma in-situ, a conventional (non-chondro id) invasive component, and areas of chondroid differentiation, as confirme d by strongly positive staining with Alcian blue at pH 2.5 and Safranin O. Immunohistochemically, one case expressed S-100 protein and vimentin, and d id not express gp100 (HMB-45), tyrosinase, MART-1, the Mel-5 antigen, the N KI/C3 antigen, CD45Ro, cytokeratin, or desmin. Electron microscopy of the c hondroid component revealed occasional tumor cells with rare, membrane-boun d, electron-dense organelles; the extracellular compartment showed amorphou s ground substance consistent with cartilaginous differentiation. Conclusions: Chondroid change in the absence of osteogenic differentiation is extremely rare in malignant melanoma. Melanoma should be considered in t he differential diagnosis of primary cutaneous neoplasms exhibiting cartila ginous differentiation.