FLT4 and lymphangioleiomyomatosis: VEGF-D is an essential factor in regulating lymphangiogenesis through binding to VEGFR-3, but also in regular angiogenesis, cardiac remodeling, and endothelial proliferation through binding to VEGFR-2/3.27, 28, 29 VEGF-D is a secreted glycoprotein, most abundantly expressed in the lungs, and together with VEGF-C and their receptor VEGFR-3, exert important biological functions in the maintenance of lymphatic vessels including lymphatic sprouting and drainage as well as homeostasis of tissue fluid.30, 31 In lymphangioleiomyomatosis, plasma VEGF-D is used as a diagnostic and a severity marker.32