HHLA2 and nonpapillary renal cell carcinoma: Similar with the expression pattern of HHLA2 at mRNA expression level from TCGA data, the staining intensity of HHLA2 in human ccRCC tissues was significantly higher than that in adjacent normal tissues (Fig. 2c), and the overall survival rate of ccRCC patients with low HHLA2 expression was significantly higher than that of the patients with high HHLA2 expression (HR = 3.141, 95% CI 1.831–9.238, P = 0.007, Fig. 2d).