PDCD1 and neoplasm: Evidence suggests that chemotherapy can enhance the anti-tumor effects of PD-1 inhibitor by reducing the number of tumor cells, promoting immunogenic tumor cell death, consuming immunosuppressive cells, increasing the number and activity of anti-tumor immune effector cells, and enhancing the secretion of cytokines that promote immune cell proliferation (Principe et al., 2022; Zhu et al., 2022).