The failure of irofulven to show clinical benefit in this limited set of thirteen renal cell carcinoma patients may be due to the fact that patients were not selected according to the two criteria for irofulven activity: NER deficiency and the expression of PTGR1. According to these criteria, we estimate that approximately one in ten ccRCC patients may respond to irofulven. This evidence concerns the gene PTGR1 and nonpapillary renal cell carcinoma.