WEE1 and neoplasm: Regorafenib is an oral multikinase inhibitor that blocks the activity of protein kinases involved in angiogenesis, oncogenesis, metastasis, and tumor immunity.276,277 Limited studies have indicated that regorafenib can reverse drug resistance caused by CSCs: regorafenib treatment decreased the stemness phenotypes including tumor sphere formation and the SP fraction of HCT-116R and DLD-1R cells.