FGFR3 and renal pelvis/ureter urothelial carcinoma: However, whereas the most prevalent FGFR3 hotspot mutation in sporadic UTUC was S249C (26 [63%] of 41 mutations; 13 of 22 and 13 of 19 for low- and high-grade tumors, respectively), in LS-UTUC, the FGFR3 mutations noted were predominantly R248C (nine [82%] of 11 mutations; four of four and five of seven for low- and high-grade tumors, respectively) and to a lesser extent G380R (four [36%] of 11 mutations; two of four and two of seven for low- and high-grade tumors, respectively; Fig 2A).