Immunohistochemical localization of S-100 protein and its subunits in melanotic lesions in the oral mucosa and skin.

Immunohistochemical localization of S-100 protein, S-100 alpha and beta subunits was examined in 23 pigmented nevi, 20 malignant melanomas and 8 metastatic melanomas originating from the oral mucosa and skin. Primary oral mucosal melanomas demonstrated no beta subunit immunoreactivity while one metastatic lesion from oral melanoma that showed only a small number of melanoma cells reacted with the beta subunit. In contrast, most cutaneous melanomas and their metastatic lesions showed immunoreaction with the S-100 beta subunit. As for pigmented nevi, immunoreactions with the three antibodies were frequently detected regardless of the site. The differences in the expression of S-100 protein beta subunit between cutaneous and mucosal melanomas may be related to differences in inductive interactions between the melanoma cells and the connective tissues and skin and mucosa.