FAS, FAS ligand, tumor infiltrating lymphocytes, and macrophages in malignant melanoma: an immunohistochemical study

Background FAS and its ligand, FASL, have important roles in the neoplasia-immunity relationship. In melanoma, the importance of FAS and FASL remains controversial, despite a group of studies. In this study, we aimed to demonstrate the distribution of FAS/FASL in melanotic lesions and to investigate the correlation between tumor infiltrating lymphocytes and macrophages. Methods Ten intra-dermal nevi, 12 primary malignant melanoma, and eight skin and 15 lymph node metastases were included in this study. FAS and FASL were studied in all of the groups using classical labeled streptavidin-biotin immunohistochemical method. Tumor infiltrating lymphocyte status and macrophage number demonstrated by CD68 immunostain were also evaluated in primary melanoma and skin metastases. Results FAS positivity was detected in all of the cases. FASL expressions were seen in 60% of the intra-dermal nevus and in all of the other groups. There were significant differences in FASL between nevus and primary melanoma, nevus and skin metastasis, and nevus and lymph node metastasis. There were strong positive correlations between FAS expression and intra-neoplastic macrophage score and between FASL and density of lymphocyte infiltration in skin metastases. Conclusion Although FAS and FASL expression is a constant feature of melanotic lesions, its diagnostic importance is very limited because of the different results obtained in the past studies. The correlation between FAS status and macrophage number and between FASL status and lymphocyte number in skin metastasis but not in primary lesions might point to diverse FAS/FASL interaction between neoplastic cells and macrophages in the different microenvironments.