Oral melanocytic lesions: differences in expression of HMB‐45 and S‐100 antigens in round and spindle cells of malignant and benign lesions

Immunohistochemistry and melanin bleaching were used to assess the expression of antigens identified by anti‐S‐100 and anti‐HMB‐45 antibodies on melanomas and intramucosal and blue nevi from the oral mucosa of 18 patients. Both antibodies reacted with cells in all three types of lesions, but there were differences in the expression of these antigens between the round and spindle cells within the lesions. In melanomas composed of round cells, the intensity and distribution of staining with HMB‐45 was greater than with S‐100. The opposite was true in melanomas composed of spindle‐shaped cells, and one spindle‐cell melanoma was HMB‐45‐ncgativc. The round cells of intramucosal nevi expressed S‐100 more intensely and more frequently than HMB‐45. The spindle‐shaped cells of blue nevi strongly expressed both S‐100 and HMB‐45. Whereas intradermal nevi from the skin do not express HMB‐45. intramucosal nevi consistently express this antigen in the lesion and overlying mucosa. Oral melanomas composed of round and spindle‐shaped cells show differences in their expression of S‐100 and HMB‐45 antigens, making the use of both antibodies complementary in the diagnosis of undifferentiated tumors.