The discovery of angiogenesis inhibitors raises the question of whether such molecules might therapeutically halt or restrain cancer's growth. Researchers have addressed this question in numerous experiments involving animals. In one striking study, mice with several different kinds of cancer were treated with injections of endostatin. After a few cycles of treatment, the initial (primary) tumor formed at the site of the injected cancer cells almost disappeared, and the animals did not develop resistance to the effects of endostatin after repeated usage.