FLT4 and cancer: Lymphatic system markers which have been used for studying the mechanism of lymphatic metastasis for several kinds of malignant tumors recently include lymphatic endothelial markers and lymphatic endothelial growth factors, and the lymphatic endothelial markers mainly include lymphatic vessel endothelial hyaluronic acid receptor–1 (LYVE–1), vascular endothelial growth factor receptor 3 (VEGFR–3), Podoplanin, and Prox–1 [1, 2].