PDGFRA and neoplasm: Meanwhile, if αPE and αEP are both negative, the proportion with both genes amplified will decrease, as the EGFR and PDGFRA amplified sub-populations compete with one another; this is likely to result in each amplified population occupying distinct regions of the tumour or one population dominating, depending on the strength of the competitive interactions and various other factors, such as one population being introduced and becoming established before the other.