PDCD1 and cancer: Despite the significant effects of PD-1/PD-L1 tumor immunotherapy in prolonging patient survival and improving the prognosis of advanced cancer patients, the development of PD-1/PD-L antibodies in tumor immunity will also face more challenges, such as resistance developed from long-term use of PD-1 or PD-L1 inhibitors, how to improve drug utilization, and how to select the best combination therapy.