CD44v6 proteins contain an exon v6-encoded region that can interact with the other major cytokines produced by the tumor microenvironment and with receptor tyrosine kinases (RTKs), such as c-Met, Ron, and vascular endothelial growth factor receptor 2 (VEGFR-2): Therefore they function as coreceptors, which plausibly explains how CD44v6 drives tumor progression and metastasis [33,34,35]. This evidence concerns the gene NTRK1 and neoplasm.