Apoptosis, Fas and Fas-ligand expression in melanocytic tumors

Impaired regulation of apoptosis is known to be associated with the development of various forms of cancer. Fas binding to its ligand, Fas ligand (Fas-L), has been shown to trigger apoptosis in various cell types. Fas-L is expressed by melanoma cells and has been suggested to play a role in melanoma escape from immune surveillance. In the present study, we assessed apoptotic activity and examined Fas and Fas-L expression in malignant melanomas, Spitz nevi and ordinary melanocytic nevi. We evaluated apoptotic activity using terminal deoxynucleotidyl transferase (TdT)-mediated dUTP nick end labeling. Apoptotic activity was found to be minimal in melanomas and moderate in Spitz nevi. In contrast, common nevi demonstrated significant levels of apoptosis in the deep parts of the tumor. Fas was found to be expressed by all Spitz nevi, most melanocytic nevi and approximately half of the malignant melanoma specimens. Fas expression was also significantly more pronounced in Spitz nevus cells as compared with the two other tumors. The anti-Fas-L antibody was found to stain all three melanocytic tumors. Staining was shown to be stronger and more frequent in melanoma cells as compared to the nevus cells. Using the Spearman test, no significant correlation between Fas-L expression in melanoma cells and apoptosis in MM-infiltrating mononuclear cells was found, suggesting that Fas-L expression in melanoma cells may not be instrumental in their ability to escape immune mechanisms of defense. In contrast, increased levels of apoptosis in the deep parts of melanocytic nevi may reflect and possibly contribute to their benign nature.