Endostatin is a naturally-occurring 20-kDa C-terminal fragment derived from type XVIII collagen. It is reported to serve as an anti-angiogenic agent, similar to angiostatin and thrombospondin.

Endostatin is a broad spectrum angiogenesis inhibitor and may interfere with the pro-angiogenic action of growth factors Endostatin is a natural antiangiogenic protein that has been shown to inhibit the growth of blood vessels, thereby starving cancerous tumors. In preclinical studies, the repeated administration of Endostatin consistently shrank primary tumors and, unlike traditional chemotherapy, showed no drug resistance over time.Endostatin is currently being studied as part of cancer research.In a Phase I clinical trial of Endostatin of the 19 patients treated, 12 were switched out of the trial by their physicians due to continued progression of their disease.In a Phase II clinical trial of Endostatin forty two patients with pancreatic endocrine tumors or carcinoid tumors were treated.A phase III clinical trial was carried out on 493 histology or cytology confirmed stage IIIB and IV NSCLC patients with a life expectancy >3 months.