PDCD1 and cancer: After the first attempt at using the immune system for cancer therapy in the late 19th century, immune-oncology or immunotherapy has been developed continuously and has become an anticipated field, as evidenced by the Nobel prize for physiology or medicine being awarded T-cell to Drs. Allison and Honjo in 2018 for the discovery of T-cell immune checkpoints, such as CTLA-4 and PD-1 [15,16].