PECAM1 and digestive system neoplasm: The effect of NGR-Dau conjugates and free Dau on vascularization in the primary tumor was evaluated by counting CD31 (endothelial marker) stained blood vessels per field of view in subcutaneous Kaposi’s sarcoma and orthotopic HT-29 human colon primary tumors, and by determining blood vessel density and number of blood vessels per mm2 (Fig. 7c,d).