PDCD1 and neoplasm: Chemotherapy is believed to improve the antitumor effect of PD-1 inhibitors by reducing the number of tumor cells, promoting the death of immunogenic tumor cells, depleting immunosuppressive cells, increasing the number and activity of antitumor immune-effector T cells, and enhancing the secretion of cytokines promoting the proliferation of immune cells (Salas-Benito et al., 2021; Principe et al., 2022).