PDGFRB and neoplasm: PDGFRB receptors are highly expressed on IGR-N91 cells with normal copy numbers of the PDGFRB gene, and their regorafenib mediated reduction and its associated induction of apoptotic cell death suggest that PDGFRB signaling may be implicated in the survival of these cells and its inhibition may represent an additional mechanism by which regorafenib induced anti-tumor effects in this model.