FLT4 and lymphangioleiomyomatosis: The various isoforms of VEGF (-A, -B, -C, and -D) have different implications: VEGF-A: a growth factor that stimulates migration and replication of endothelial cells; VEGF-B: a vascular growth factor that acts as an antioxidant and downregulates pathological angiogenesis [9]; VEGF-C: a lymphatic vessel growth factor (promoting lymphangiogenesis) [10]; and VEGF-D: a ligand for lymphatic growth factor receptor VEGFR-3/Flt-4 that can also act as a malignancy biomarker (i.e., sporadic lymphangioleiomyomatosis) [11].