PDCD2 and head and neck squamous cell carcinoma: Next, we combined the TCGA and GTEx database, and the results confirmed that PDCD2 expression was significantly higher in GBM, GBMLGG, brain lower grade glioma (LGG), UCEC, BRCA, LUAD, stomach and esophageal carcinoma (STES), COAD, PRAD, STAD, head and neck squamous cell carcinoma (HNSC), LUSC, LIHC, skin cutaneous melanoma (SKCM), THCA, rectum adenocarcinoma (READ), esophageal carcinoma (ESCA), ovarian serous cystadenocarcinoma (OV), pancreatic adenocarcinoma (PAAD), testicular germ cell tumors (TGCT), uterine carcinosarcoma (UCS), and CHOL than in paired adjacent normal tissues (Fig. 1B).