inside your abdominal cavity is the long tubular digestive tract. the second part of this tube -- the large intestine -- is composed of the colon which stretches four to six feet and the rectum which is only four to six inches long. the inner lining of this "colorectal tube" can be a fertile breeding ground for small tumors called polyps (figure 1). about a quarter of all adults in the u. s. over the age of 50 will have at least one colorectal polyp. most colorectal cancers develop from polyps in glandular tissue of the intestinal lining. most polyps are benign but at least one type is known to be precancerous. these are called adenomatous polyps. the size of the polyp correlates with the development of cancer. polyps less than 1 cm in size have a slightly greater than a 1% chance of becoming cancer but those 2 cm or greater have a 40% chance of transforming into cancer. overall the incidence is about 5%. most colorectal cancers develop from polyps in glandular tissue of the intestinal lining. if colorectal cancer is diagnosed and treated early while the tumor is still localized the disease is highly curable with five-year survival rates of about 90%. if the tumor continues to grow cancer can spread directly through the bowel wall to surrounding lymph nodes tissues and organs as well as into the bloodstream. once the cancer spreads to lymph nodes or other organs successful treatment becomes more difficult. depending on how advanced the disease is five-year survival rates range from 9% to 93%. cancers of the colon and rectum are the third most common cancer in the u. s. with approximately 150 000 cases diagnosed each year. like many cancers colorectal cancer is of particular concern for people older than age 50. although diagnosis is often possible at an early stage many people delay seeking medical care because they are embarrassed or fearful of symptoms related to their bowels. risk increases significantly after age 50 and continues to increase with age.
what is colorectal cancer?