NTRK1 and cancer: Within the tumor microenvironment, decorin directly engages and down-regulates multiple receptor tyrosine kinases including the epidermal growth factor receptor (EGFR), the HGF receptor Met, the IGF-I receptor (IGFIR), the VEGF receptor (VEGFR) and the PDGF receptor (PDGFR), often overexpressed in cancer cells [31,35,36].