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This is the VOA Special English Science Report.

Scientists say they have made an important discovery about how a cancerous tumor develops the blood supply that it needs. The researchers found that cells from the bone marrow play an important part in creating the blood supply. Marrow is the soft tissue found inside most bones.

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The research was carried out by scientists at the Weill Medical College of Cornell University and Memorial Sloan-Kettering Cancer Center in New York City. They reported the results of their studies in the publication "Nature Medicine."

The scientists used mice to investigate the theory that special stem cells from the bone marrow are involved in creating new blood vessels for cancerous growths. They used mice that had been genetically engineered so they could not produce new blood vessels. The mice also could not develop cancer because tumors placed in them could not make new blood vessels.

The researchers placed specially marked bone marrow from normal mice into the mice that could not produce blood vessels. The mice were then given a kind of cancer cell that spreads quickly. The researchers found that cancerous tumors appeared on the mice. After the animals died, the researchers found the marked bone marrow cells in most of the tumors.

Cancerous tumor cells produce a protein called VEGF (VEJ-eff). VEGF helps blood vessels grow into the tumor. The researchers found that the cells used by VEGF to build blood vessels come from the bone marrow. They include two kinds of stem cells. One kind is involved in the development of blood vessel walls.

VEGF makes these cells leave the bone marrow, enter the bloodstream and seek out the tumor. Then the cells begin to create blood vessels that support the tumor. The tumor then increases in size and destroys normal tissue.

The scientists found that they could stop the action of VEGF on the bone marrow stem cells with specially made substances called antibodies. The antibodies blocked the action of the stem cells. In the mice experiments, the use of two kinds of antibodies caused the cancer cells to die.

Other researchers say this work shows a new way of thinking about a tumor's blood supply. They say these kinds of antibodies may provide a new way to attack cancer.

This VOA Special English Science Report was written by Nancy Steinbach.