PDCD1 and gastric cancer: In addition, we explored the relationship between the EFNA family genes and the immune microenvironment (B cells, M2 macrophages, monocytes, CD8+ T cells, regulatory T cells, myeloid dendritic cells, natural killer cells, non-regulatory CD4+ T cells), immune checkpoint (PDCD1, PDCD1LG2, CD274, CTLA4), and IC50 of common chemotherapeutic drugs for gastric cancer (5-fluorouracil, cisplatin, docetaxel and gemcitabine).