FGFR1 and neuroblastoma: Regorafenib treatment also inhibited 13-cis-retinoic acid-induced RET phosphorylation, and led to reduced expression of FGFR1 and PDGFRβ, with incomplete inhibition of FGFR1 and PDGFRβ phosphorylation also noted in tested neuroblastoma cell lines (Fig. 3b, Supplemental Fig. 4).