PDCD1 and neoplasm: The results of a study conducted by Fucikova et al. reflect a strong correlation between the density of CD8+ T cells infiltrating the tumor and the number of LAG-3+, CTLA-4+ and PD-1+ cells within the tumor, suggesting that PD-1, CTLA-4 and LAG-3 behave as T cell markers in the tumor environment [93].