KIT and gastrointestinal stromal tumor: In our PDX models, the degree of KIT signaling inhibition by sunitinib and regorafenib was also similar to observations made in the two cell lines above; i.e., it showed slight inhibition of KIT signaling by sunitinib and marked inhibition by regorafenib in the GIST-RX1 and GIST-T1/816 models.