FSTL1 and nonpapillary renal cell carcinoma: In ccRCC tissues, FSTL1 expression was positively correlated with HIF-1α (Spearmen r = 0.216, P = 0.047) but negatively correlated with HIF-2α expression (Spearmen r = − 0.229, P = 0.044) (Table 3).