PDGFRB and cholangiocarcinoma: Regorafenib inhibits angiogenic (VEGFR-1–3, TIE2) and stromal (PDGFR-β, fibroblast growth factor receptor 1 or FGFR1) factors that promote tumor vessel formation and suppresses several oncogenic kinases (KIT, RET, RAF) [56] and has shown promising results in advanced refractory CCA [47,57].