Evidence-based colorectal cancer (CRC) screening guidelines separately developed and recently revised by the American Cancer Society and the US Multisociety Taskforce on Colorectal Cancer recommend that all asymptomatic, average-risk women and men be offered screening for CRC beginning at age 50 using one of five screening options:
annual fecal occult blood tests (FOBT);
flexible sigmoidoscopy (FS) every five years;
the combination of FOBT and FS;
double-contrast barium enema every five years; or
colonoscopy every 10 years.
The two primary objectives of screening are to detect early, curable cancers and to detect and resect advanced adenomatous polyps before they turn cancerous. Relative to these two objectives, each of the screening options has advantages and limitations that clinicians and their patients need to consider when selecting a screening approach.
Annual FOBT Screening
FOBT is the only screening option that has been shown in randomized controlled trials to reduce both the mortality and incidence of colorectal cancer. The Minnesota FOBT Screening Trial reported in 1993 that screening asymptomatic individuals between the ages of 50 and 80 with annual rehydrated Hemoccult tests (Beckman-Coulter, Palo Alto, CA) and performing colonoscopy for those with a positive result, reduced the mortality from CRC by 33%. Investigators in this trial estimated that a screening program using their methods with 100% compliance would reduce CRC mortality by about 45% compared with that of a totally unscreened control group. The Minnesota Trial later showed that annual screening was substantially more effective in reducing mortality than was biennial screening. In addition, a program of annual screening reduced subsequent colorectal cancer incidence by 20%, presumably from detection and resection of advanced premalignant polyps. Although studies have shown that the sensitivity of a single FOBT test for detecting cancer is only 30%–50%, a program of repeated annual screening can detect up to 92% of all cancers, most of them at an early, curable stage. Other advantages of FOBT screening are its general availability and acceptability, and its very low up-front cost.The main disadvantages of FOBT screening are that frequent screening is required, it fails to detect many polyps (especially smaller ones) and some cancers (especially distal ones), and test specificity is relatively low—there are many false positive tests requiring patients without significant disease to undergo colonoscopy.
All of the large trials of FOBT screening used the guaiac-based Hemoccult test. The guidelines recommend that if Hemoccult tests are used for screening, two samples from each of three consecutive stools should be tested after following a diet free of red meat and peroxidase-rich fruits and vegetables. Rehydration, which increases the sensitivity of guaiac tests, is not recommended because it may interfere with the readability of the test and it increases falsepositivity. Newer guaiac-based and immunochemical FOBTs now are available that have greater sensitivity than standard Hemoccult tests, but also have acceptable specificity.The immunochemical tests, which now are being widely used in Japan and Australia, are still undergoing field testing in the US. These FOBTs are especially promising because they are specific for human globin and therefore are not affected by diet or medications. FOBT screening of a single stool sample obtained by digital-rectal examination—a common practice in primary care clinics—is now discouraged because such screening recently has been shown to be highly inaccurate. A positive screening FOBT should be followed by colonoscopy, no exceptions.
Flexible Sigmoidoscopy Every Five Years
Flexible sigmoidoscopy (FS) using modern 60cm endoscopes provides a highly accurate (few false- positives or false-negatives) examination of the left colon, site of most CRCs and advanced adenomas. Advantages of FS for screening are that, when performed by an experienced, well-trained examiner, it is a safe, effective, quick and inexpensive examination acceptable to most patients after a relatively simple bowel preparation. Cohort and casecontrol studies indicate that FS screening reduces mortality from CRCs within its reach by 60–85%, and the protective effect lasts for five to 10 years.The Veterans Affairs (VA) Multicenter Colonoscopy Screening Study demonstrated that endoscopy to the sigmoid colon-descending colon junction would diagnose about 70% of all advanced colonic neoplasia, provided that, if an adenoma is found in the distal colon, full colonoscopy then is performed. The main disadvantage of FS is that, because it is performed without sedation, it is poorly tolerated by many patients, and the examination performed alone will miss about 30% of advanced neoplasia located proximal to its reach.
John H Bond, MD, is Professor of
Medicine at the University of
Minnesota Medical School, and chief
of the Gastroenterology Section at
the VA Medical Center, Minneapolis,
Minnesota. Dr Bond's current
research activities include studies of
screening, early diagnosis, and
prevention of colorectal polyps and
cancer. He was a co-director of the
long-term Minnesota fecal occult
blood screening trial and a coinvestigator
in the National Polyp
Study. He is currently a coinvestigator
in the VA Cooperative
Colonoscopy Screening Trial, the US
National Colonoscopy Screening Trial,
and two National Cancer Institute
(NCI) polyp chemoprevention studies.
He chaired the American Digestive
Health Foundation's Public Awareness
Campaign for Colorectal Cancer, a
multisociety program designed to
educate the public and primary care
physicians about the impact of
colorectal cancer in the US and the
value of screening, and is a member
of the National Colorectal Cancer
Roundtable and the Multi-society
Task Force for Colorectal Cancer
Screening. Dr Bond is an active
member of a number of professional
medical societies and is pastpresident
of the American Society
for Gastrointestinal Endoscopy
(ASGE). He recently served for six
years as chairman of the editorial
board of the journal Gastrointestinal
Endoscopy. He has authored over
250 papers and book chapters
dealing with gastrointestinal
disorders. A graduate of Harvard
College and the University of
Pennsylvania School of Medicine, he
completed his residency in internal
medicine and fellowship in
gastroenterology at the University of
Minnesota Hospital.
Send Article Feedback
Add me to mailing list
I Agree to terms and conditions
Order Reprint
Order high-quality repints of any articles on this website
