Protein tyrosine kinases (PTKs) are enzymes that catalyze the transfer of phosphate groups from ATP molecules to tyrosine residues of their substrates. PTKs can be divided into receptor tyrosine kinases (RTKs) and nonreceptor tyrosine kinases. In humans, there are 32 nonreceptor tyrosine kinases and 58 RTKs. RTKs can further be divided into 20 subfamilies depending on their domain arrangements (Lemmon and Schlessinger 2010). They are important components of cellular signaling pathways and regulate cell proliferation, survival, differentiation, metabolism, and motility. Because of their role in cellular signal transduction pathways, genetic changes that affect RTK activity can result in various diseases. RTKs are therefore attractive drug targets in many diseases including cancers. Among 20 RTK subfamilies, the type III receptor tyrosine kinase family, including platelet-derived growth factor receptors (PDGFA and PDGFB), colony...