Identifying VM and EDV in human sample of LSCC by CD31and PAS double staining. A.) The VM channel (black arrow) in human sample is formed by laryngeal cancer cells. There are red blood cells in the center of the channel. PAS-positive substances line the channel and form a basement membrane-like structure (pink). Note the absence of necrosis and hemorrhage in the tumor tissue near the VM channel (original magnification: ×400). B.) Endothelium-dependent vessels (black arrows) are lined by spindle-shape endothelial cells, which are stained by CD31 (brown). The vessels' basement membrane is positive for PAS staining (pink) (original magnification: ×400).