RRM2 and head and neck cancer: In paired tumor and normal tissues from the TCGA pan-cancer database, RRM2 was highly expressed in bladder urothelial carcinoma (BLCA), breast invasive carcinoma (BRCA), cholangiocarcinoma (CHOL), colon adenocarcinoma (COAD), thyroid carcinoma (THCA), uterine corpus (UCEC), esophageal carcinoma (ESCA), head and neck cancer (HNSC), kidney renal papillary cell carcinoma (KIRP), rectum adenocarcinoma (READ), stomach adenocarcinoma (STAD), LIHC, lung adenocarcinoma (LUAD), lung squamous cell carcinoma (LUSC) and prostate adenocarcinoma (PRAD) (Fig. 1B).