The most frequently mutated genes in the 17 LS-UTUC tumors (present in > 10 patients) in decreasing frequency were KMT2D, CREBBP, ARID1A, SMARCA4, CIC, FAT1, FGFR3, FOXP1, KMT2C, NOTCH1, and NOTCH3 (Appendix Fig A2). The gene discussed is FGFR3; the disease is renal pelvis/ureter urothelial carcinoma.