BGJ398 was administered orally at 125 mg/day on a 3 weeks on, 1 week off schedule until unacceptable toxicity or progression….Given the rather heterogeneous array of alterations observed in this cohort, it is challenging to draw any firm conclusions regarding the nature of FGFR3 alterations and response to BGJ398....FGFR3 resistance mutations, including FGFR3 gatekeeper mutations (V443L, V443M, and L496V), as determined by preclinical studies, were detected in the cfDNA of four patients during treatment.