CTLA4 and head and neck squamous cell carcinoma: Among the 33 cancer types in TCGA, PD-1 and CTLA4 levels were upregulated in tumor tissues relative to matched non-carcinoma tissues in uterine corpus endometrial carcinoma (UCEC), cholangiocarcinoma (CHOL), breast cancer (BRCA), head-neck squamous cell carcinoma (HNSC), esophageal carcinoma (ESCA), kidney renal papillary cell carcinoma (KIRP), kidney renal clear cell carcinoma (KIRC), lung adenocarcinoma (LUAD), LIHC, and stomach adenocarcinoma (STAD); whereas both were downregulated in kidney chromophobe.