Prof. Yaron Niv, Director of the Institute of Gastroenterology at Rabin Medical Center, along with his colleague and friend, Dr. C. Richard Boland, Chief of gastroenterology at Baylor University, have identified a virus that exists in 90 percent of colon cancer cases in Israel. This normally harmless virus, called JC, is present in 70 to 80 percent of all human beings. But until now, it was not known what triggers change in the genetic structure of the large intestine that enables the cancer to develop. Prof. Niv and Dr. Boland studied hundreds of Israeli patients with colon cancer, looking at their cancer tissue for DNA sequences of the JC virus in the cancer cells. They found that more than 80 percent of those tested had the DNA for the JC virus. The JC virus - or more specifically the T-antigen protein that is synthesized by the virus - may be the trigger in the development of at least 20-40 percent of the cases of colorectal cancer.