Since we observed that growth of HDMEC on the tumor-associated matrices collagen I and tenascin C impaired the ability of the anti-angiogenic molecules to inhibit VEGF-induced proliferation, we next examined whether growth on collagen I influenced the ability of the angiostatic molecules to induce apoptosis of endothelial cells, by examining the proportion of cells in sub-G1 following staining with propidium iodide as a measure of apoptotic cells. Here, TNC is linked to neoplasm.