Molecules that block angiogenesis, such as the well-known endostatin, can therefore choke tumors and are being investigating as anticancer drugs in humans. The researchers first injected mice with melanoma cells, which form large tumors within a few days. Then they observed that tumor growth was dramatically reduced when the same mice were infected with Toxoplasma gondii , the parasite that causes toxoplasmosis. The infection also blocked cancer growth when the animals' immune systems were severely impaired by genetic defect, proving that immunity did not play a major role in inhibiting the tumors. Moreover, mice with toxoplasmosis failed to develop new blood vessels, even after they were injected with strong stimulators of angiogenesis.
Scientists believe that mice produce powerful antiangiogenic factors in response to the infection.
As exciting as these results are, the scientists do not know whether a new molecule or well-known compound is stopping the blood vessel growth in the mice, and they stress that it may take years to answer that question.