At least three potential Lynch syndrome vaccines are in development, including two in early clinical trials in the U.S. and a third beginning in Britain. Colorectal cancer is the most common consequence. About 158,000 people are diagnosed with colorectal cancer in the U.S. each year, most of them over 50. Lynch syndrome affects about 1 in 279 people. For the average person, U.S. guidelines call for routine colorectal cancer screening — with a colonoscopy or other kinds of tests — to begin at age 45.