VEGFA and neoplasm: Second, both CD44s and CD44v splice variants have been shown to act as a co-receptor to receptor tyrosine kinases (RTK), such as Met or the Epidermal Growth Factor (EGF) family ErbB, as well as stabilize other RTK complexes, such as receptors for vascular endothelial growth factor (VEGFR), which under pathological conditions leads to tumor progression, metastasis, and angiogenesis.