FSTL1 and nonpapillary renal cell carcinoma: In our previous study investigating global gene expression profiling in RCC cells with different metastatic potentials, we showed that follistatin-like 1 (FSTL1) was significantly down-regulated in metastatic ccRCC compared to primary ccRCC cells; furthermore, the mRNA levels of FSTL1 were also significantly lower in ccRCC tissues than in adjacent renal tissue14.