In order for tumors to grow and spread to other parts of the body, they need to have a growing blood supply. Tumor cells have been shown to produce substances that stimulate the abnormal growth of new blood vessels that allow the tumor to grow. In adults, blood vessel cells normally divide very rapidly. It is thought that PTK787/ZK222584 may interfere with the growth of new blood vessels. A drug that interferes with the growth of new blood vessels might stop tumor growth, and possibly shrink the tumor by keeping it from receiving nutrients and oxygen supplied by the blood vessels. Since normal blood vessel cells divide very rarely, it might be possible to stop tumor growth without harming normal tissues.