PDCD1 and gastric cancer: By analyzing genes that were differentially expressed between gastric cancer patients who responded well to PD-1 inhibitors and those who did not respond to PD-1 inhibitors, we find C-X-C Motif Chemokine Receptor 2 Pseudogene 1 (CXCR2P1), a pseudogene encoding long non-coding RNA (lncRNA) which may affect cell phenotype through microRNA according to the previous research, plays a key role in the response of gastric cancer cells to PD-1 inhibitor (8).