SLC44A2 and papillary renal cell carcinoma: Among the 26 TCGA cancer types, SLC44A2 was significantly downregulated in lung adenocarcinoma (LUAD), lung squamous cell carcinoma (LUSC), renal papillary cell carcinoma (KIRP), renal clear cell carcinoma (KIRC), prostate adenocarcinoma (PRAD), and head and neck squamous cell carcinoma (HNSC) (Fig. S1A).