Primary malignant tumors produce as-yet unidentified factors that induce microvascular endothelial cells to express CEACAM1. Upon tyrosine phosphorylation of the cytoplasmic domain of CEACAM1-L, intracellular signals that up-regulate the expression of Prox1 are produced, leading in turn to production and surface expression of VEGFR-3. Expression of CEACAM1-L also induces expression of VEGF-C, VEGF-D, podoplanin, and LYVE-1, turning the cells into lymphatic endothelial cells. VEGF-C and VEGF-D activate VEGFR-3 in an autocrine loop, stimulating the reprogrammed cells to grow into lymph vessels.