Bone marrow-derived hematopoietic progenitor cells that express VEGFR1 home to tumor-specific pre-metastatic sites and form cellular clusters before the arrival of tumor cells [52], while the metastatic ability of primary tumors is increased by permanent exosomal education of bone marrow progenitor cells via the receptor tyrosine kinase MET [53]. This evidence concerns the gene NTRK1 and neoplasm.