NDRG1 and nonpapillary renal cell carcinoma: Closer analysis of these cases revealed that of the 58 trees showing poor performance against the ccRCC datasets, 42 share a common structure that includes only three genes organized in two levels, with ANKRD37 being the root nodes and two branches, one evaluating NDRG1 and the other BHLHE40 (Additional file 4: Fig. S1A).