KIT and gastrointestinal stromal tumor: Out of 3 KIT inhibitors, the combination of sunitinib or regorafenib with PD was more effective than the combination of imatinib+PD, suggesting that MAPK signaling plays an important role in GIST cell survival and a combination of MEK inhibitors with 2nd and 3rd line KIT inhibitors might be a more effective strategy to overcome resistance.