The most common AE was hyperphosphatemia (72%), with 25% of patients experiencing grade 3 or 4 hyperphosphatemia.29 Hyperphosphatemia may be an on-target effect related to FGF23-regualted phosphate homeostasis.30,31 INCB054828, a pan-FGFR1/2/3 inhibitor with half-maximal activity of 3–50 nM in FGFR-dependent cell viability assays with >30-fold selectivity over FGFR-independent cell lines, has reported preliminary clinical activity in a small cohort of CCA patients,32 and has now progressed into phase 2 development (NCT02924376). This evidence concerns the gene FGF23 and hyperphosphatemia.