NTRK1 and cancer: VEGF-A and PIGF, which are major pro-angiogenic factors associated with cancer angiogenesis and are pro-tumorigenic and Flt-1, also known as vascular endothelial growth factor receptor 1 (VEGFR-1), is a high-affinity tyrosine kinase receptor for VEGF involved in tumor growth and metastasis (46).