Regarding CRC, the cytotoxic T-lymphocyte-associated antigen 4 (CTLA-4), the programmed cell death protein 1 (PD-1), the lymphocyte-activation gene 3 (LAG3), the mucin domain-3-containing molecule 3 (TIM-3), and Indoleamine 2,3-dioxygenase (IDO) are recognized as significant inhibitory checkpoints that may play an important role in the growth and progression of tumors. The gene discussed is PDCD1; the disease is colorectal carcinoma.