PDCD1 and colorectal carcinoma: First, a correlation analysis between the TFS and immune checkpoint proteins, including CTLA4, PD-1, PD-L1, lymphocyte activation gene-3 (LAG-3), T cell immunoglobulin and immunoreceptor tyrosine-based inhibition motif domain (TIGIT), and T cell immunoglobulin-3 (TIM-3), in the 516 CRC patients in the TCGA dataset was performed.