PDCD1 and colorectal carcinoma: Further research indicates that CRC cells within an active T helper 1 (Th1)/cytotoxic T lymphocyte (CTL) immune microenvironment tend to express high levels of various immunosuppressive‐related molecules, including PD‐1, CTLA‐4, lymphocyte activation gene 3 (LAG‐3), and T cell immunoreceptor with Ig and ITIM domains (TIGIT) [21].