PDCD1 and cancer: In recent years, researchers have also found that CDK4/6 inhibitors improve the tumor immune microenvironment and enhance T-cell activity, and have been found to significantly increase the antitumor effect when combined with PD-1/PD-L1 inhibitors in a variety of animal models of cancer (168, 170).These studies also illustrate the potential of combining the two in the future treatment of cancer.