HAVCR2 and neoplasm: In addition to PD-1/PD-L1, substantial evidence suggests that a variety of other inhibitory checkpoint molecules might exist in the tumor microenvironment [e.g., B7H3 (31), IDO-1 (32), LAG-3 (33), TIM-3 (34), and VISTA (35)], which also participate in the regulation of tumor immune escape.