Little is known about the role of tPA in tumor angiogenesis; however, ex vivo cultures of aortic rings attained from tPA−/− mice and grown on Matrigel and collagen-I lattices displayed a total failure in capillary sprouting similar to that seen in vessels retrieved from Plg deficient mice confirming that tPA and Plg are essential for angiogenesis in this model. This evidence concerns the gene PLG and neoplasm.