Heparanase-mediated extravasation of blood-borne cells. Heparanase expressed by tumor cells (left) and neutrophils (right) promotes cell invasion between adjacent vascular ECs and through their underlying basal lamina (BL) into the ECM. Platelets may facilitate extravasation of blood-borne cells through binding to the invading cells, and activation and release of their own heparanase enzyme. Left: Scanning electron micrographs showing invasion of T-lymphoma cells, in the absence (top) or presence (bottom) of platelets, through a monolayer of cultured vascular ECs.