CD27 and nonpapillary renal cell carcinoma: We further explored the expression levels of these 25 genes between normal kidney tissues and ccRCC tissues by utilizing the TCGA dataset and eventually identified 10 genes including LAG3, CD27, CD44, CD86, CD276, HHLA2, LAIR1, LGALS9, TIGIT, TNFRSF14 (Additional file 2: Figure S1).