Đang chuẩn bị nút TẢI XUỐNG, xin hãy chờ
Tải xuống
Khoảng 6% dân số sống đến 80 tuổi ở Mỹ sẽ phát triển Colo-trực tràng ung thư (CRC). 90% phát triển từ u tuyến tồn tại từ trước, 75% của tổng số sẽ được lẻ tẻ với không có tiền sử gia đình, và 1% sẽ phát triển ở những bệnh nhân bị viêm loét đại tràng. | 72 CHRONIC GASTROINTESTINAL BLEEDING COLORECTAL CANCER I EPIDEMIOLOGY About 6 of the population living to the age of 80 in the USA will develop colo-rectal cancer CRC . 90 develop from preexisting adenomas 75 of the total will be sporadic with no family history and 1 will develop in patients with ulcerative colitis. Colonic cancer has an equal age sex distribution but rectal carcinoma is more common in men. The mean age of presentation of sporadic CRC is 67 years 90 develop after the age of 50 but it is lower in familial CRC. There is a wide geographic variation with rates up to 20 times higher in the Western world but countties with a previously low incidence are showing rises such as Japan where there has been a 40 increase over the last 30 years. The incidence of CRC in migrants also rapidly assumes that in the local population becoming almost equal within a generation. The distribution of CRC within the colon is also changing with a rise in the incidence of right-sided tumours Fig. 1 which means that at least 40 of tumours would not be reached by flexible sigmoidoscopy. AETIOLOGY Diet An increased incidence of CRC is recognised with a number of dietary factors such as a high meat intake low calcium vitamin D or folate intake high alochol consumption especially rectal cancer in men smoking increased fat intake and obesity. Meat when cooked at 200 C such as during grilling frying and barbecuing produces heterocyclic amines which in fast acetylators have been linked to CRC development. Factors that appear to reduce risk are a high fibre intake particularly as vegetables and use of aspirin or other NSAIDs which appear to confer protection Table 1 . The role of fibre has been recognised since the early 1970s when low CRC rates amongst Africans were attributed to their high fibre intake. However dietary fibre is non-digested plant material and contains starches and non-starch polysaccharides so the exact protective component is unclear. Although the mechanism is .
