CDK4 and neoplasm: This correlation was significant, but weak in primary tumor samples, with r = 0.3 and P = 0.041, and strengthening in recurrence, with r = 0.73 and P = 0.9 × 10–8, suggesting that co-amplification of EGFR, CDK4, and PDGFRA may allow more tumor cells to adopt this hypoxia-driven perivascular phenotype.