PDGFRA and neoplasm: Taken together, these results support that IGF1R is a key player that controls the influx of growth signals into tumor OPCs by two folds of mechanism: 1) in the context without PDGF, the activation of IGF1R can activate PDGFRα at the same time; and 2) in the context with PDGF, the action of PDGFRα requires the existence of IGF1R (as proposed in Figure 7L).