Different treatment responses might be explained by differences in specific FGFR3 driver mutation frequencies or tumor heterogeneity, as 50% of UTUC patients had an R248C mutation, compared to 12% of patients with UC of the bladder (UCB) (N = 59), while lower heterogeneity was reported UTUC patients compared to UCB patients [64]. This evidence concerns the gene FGFR3 and renal pelvis/ureter urothelial carcinoma.