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1. Cells normally divide to produce more cells only as the body needs them. This process is controlled in part by "oncogenes"--genes that direct cell growth--and by tumor-suppressor genes, which are in charge of cell death. Some cancers occur when a defective oncogene, operating in the nucleus of a cell, sends out a flood of protein signals that cause the cell to embark on a course of rapid cell division. The resulting tumor cells proliferate--urged on by growth signals in the blood stream that attach to the surface of the cells. The tumor-suppressor genes that would normally stop this proliferation either can't keep up or break down.2. One of the most important cellular signals produced by the oncogene is called epidermal growth factor (EGF). Normally in short supply, it is found in excess amounts in up to half of all types of malignant tumors. While the surface of a normal cell may have about 10,000 EGF receptors, cancer cells can have a million or more. EGF binds to its receptors on the surface of a cell and then triggers a cascade of enzymes inside that play an important role in keeping the tumor alive, well-nourished, and spreading.3. IMC-C225 is an antibody developed in the lab that identifies and locks onto the receptors of a cancer cell before EGF can reach it, in essence gumming up the trigger. The result: Growth enzymes are not activated, and the cell eventually stops dividing.