XDH and squamous cell lung carcinoma: Consistently, in TCGA, low XDH mRNA expression was significantly associated with breast invasive carcinoma (BRCA), colon adenocarcinoma (COAD), liver hepatocellular carcinoma (LIHC), and rectum adenocarcinoma (READ), while XDH mRNA expression was higher in HNSC, lung adenocarcinoma (LUAD), and lung squamous cell carcinoma (LUSC) tissues than in adjacent normal tissues (Fig. 1B).