Finally, the FGFR3 R248C hotspot mutation, which has previously been shown to be enriched in Lynch Syndrome-associated UTUC as compared to sporadic UTUC tumors26, was present in 3 of the 4 MSI-H tumor/patient-matched PDX pairs (UCC17, UCC36 and UCC34). Here, FGFR3 is linked to renal pelvis/ureter urothelial carcinoma.