The IARC Perspective on Colorectal Cancer Screening

Abstract

Colorectal cancer, which is the third most common cancer in men and the second most common in women, represents almost 10% of the annual global cancer incidence. 1 Incidence rates of colorectal cancer show a strong positive gradient with an increasing level of economic development. 2 Even so, the net 5-year rate of survival decreases with lower levels of income, with rates reaching 60% in high-income countries but falling to 30% or less in low-income countries. 3 Established risk factors for colorectal cancer include consumption of processed meats, 4 consumption of alcoholic beverages, 5 tobacco smoking , 5 and excess body fat, 6 whereas consumption of dietary fiber and dairy products and increased levels of physical activity decrease the risk. 7,8 In addition, certain subgroups of the population are at increased risk owing to genetic predisposition (e.g., the Lynch syndrome), a family or personal history of colorectal neoplasia, or medical conditions (e.g., inflammatory bowel disease) that have been associated with colorectal cancer. Colorectal cancer can be classified on the basis of the location within the large bowel, histologic characteristics, and molecular features. Advanced adenomas-in particular, those measuring more than 10 mm in diameter-are the most well-known precursor lesions of colorectal cancer. 9 Screening aims to reduce the risk of death from colorectal cancer through early detection and the rate of complications associated with detection of cancer at a later stage. Such screening also aims to reduce the incidence and mortality of colorectal cancer through detection and removal of precancerous lesions. Colorectal cancer screening is available in many countries with high and upper-middle incomes worldwide and is delivered by organized programs or through opportunistic screening. Participation rates in such screening are highly variable among countries and settings 10 but have typically been below 40%. Insurance status and access to primary care are the main determinants of participation. Additional obstacles include costs, logistic challenges, lack of provider involvement, language barriers, cultural beliefs, and lack of awareness of colorectal cancer screening. 11,12 There are several methods available for colorec-tal cancer screening. Stool-based tests to detect blood include the guaiac fecal occult blood test and the more sensitive fecal immunochemical test (FIT). 13 Endoscopic methods, which use optical approaches to directly examine the rectum and colon, include sigmoidoscopy and colonos-copy. 14 Colonoscopy is used both as a primary screening tool and as follow-up for persons who have tested positive with other screening methods. In addition, computed tomographic (CT) colonography, an imaging method based on scanning technology, has been developed as a less invasive visualization technique for colorec-tal cancer screening. 15 Newer techniques that have recently emerged but have not been widely tested are based on visual inspection (e.g., video capsule endoscopy) or the analysis of biomarkers in stool (e.g., multitarget-stool DNA), in blood (e.g., methylated septin 9 DNA), or in breath (e.g., volatile organic compounds and various markers of protein, RNA, and DNA). We reviewed the published evidence from ran-domized, controlled trials, observational studies, and modeling studies assessing stool-based, en-doscopic, and CT colonography-based screening methods and evaluated outcomes with respect to preventive effects, adverse effects, and the balance of benefits and harms in average-risk populations of men and women combined. (Details regarding the working procedures that were used for conducting the review and a list of the members of the International Agency for Re-The New England Journal of Medicine Downloaded from nejm.org by Fabio Levi on May 2, 2018. For personal use only. No other uses without permission.