PIWIL4 and nonpapillary renal cell carcinoma: To identify clear-cell renal cell carcinoma-associated PIWI-interacting RNA that could be involved in tumorigenesis, we firstly analyzed the expression profiles of piRNAs from The Cancer Genome Atlas (TCGA), which contains 529 ccRCC tissues and 71 adjacent normal tissues, which was characterized by Martinez, et al. [20].