A new study has answered a question that has puzzled cancer researchers for decades: Does a genetic defect found in nearly all human colorectal cancers simply accompany the disease, or does it trigger its development? A team led by Harvard Medical School researchers at Beth Israel Deaconess Medical Center showed that replicating the genetic defect by deleting a single gene called COSMC (C1GalT1C1) in cells lining the intestines of mice led to the development of invasive colorectal cancer within a year.