Routine screening for colorectal cancer has been shown to reduce mortality.1 However, only 44% of Americans over the age of 50 years have been screened.2
Here are the highlights of recently updated guidelines for colorectal cancer screening from the American Gastroenterological Association.3 Among the changes that have been made since the previous guidelines were released in 1997 are:
Rehydration of fecal occult blood is not recommended.
The screening interval for double-contrast barium enema (DCBE) has been shortened to 5 years.
Colonoscopy is the preferred diagnostic test for patients with findings on screening and is the recommended screening test for those with a family history of hereditary nonpolyposis colorectal cancer (HNPCC).
The recommended interval for the first follow-up colonoscopy after polypectomy has been lengthened from 3 to 5 years for patients who are at low risk.
DETERMINATION OF RISK STATUS
First, obtain a complete history to determine whether the patient is at average or increased risk. Patients older than 50 years who do not have any risk factors are at average risk for colorectal cancer. One or more of the following factors places a patient at increased risk:
History of colorectal cancer or adenomatous polyp.
Inflammatory bowel disease or other condition with a predisposition to colon cancer.
Family history of colon cancer or adenomatous polyp (2 or more first-degree relatives; 1 first-degree relative younger than 60 years affected).
Advise patients who have an abnormal result from any screening test to undergo further evaluation by colonoscopy (if colonoscopy is not available, flexible sigmoidoscopy and DCBE are alternatives).
PATIENTS AT AVERAGE RISK
Screening guidelines for patients at average risk for colorectal cancer are listed in Table 1.
Fecal occult blood test. For patients older than 50 years, recommend a guaiac-based fecal occult blood test (FOBT) yearly. To increase effectiveness, test 2 samples from 3 consecutive stools without rehydration. Dietary restrictions (avoidance of red meat) are advised for sensitive guaiac-based tests but are unnecessary in immunochemical and less sensitive guaiac-based tests.
Sigmoidoscopy. Recommend a flexible sigmoidoscopy every 5 years. A flexible sigmoidoscopy is less sensitive than a colonoscopy and, therefore, a shorter interval between tests is advised.
Combined FOBT and flexible sigmoidoscopy. Combine the annual FOBT with a flexible sigmoidoscopy every 5 years. When both tests are performed in the same year, complete the FOBT first.
Colonoscopy. Recommend a colonoscopy every 10 years. This interval is based on the sensitivity of the test and the rate at which advanced adenomas develop (an average of 10 years4,5).
Double-contrast barium enema. Offer a DCBE every 5 years to patients who did not have a flexible sigmoidoscopy. DCBE is less sensitive than colonoscopy, but it is included in the guidelines because it examines the entire colon, detects half of all large polyps,6 and is widely available. Recommend a colonoscopy for patients with abnormal DCBE results.
PATIENTS AT INCREASED RISK FROM FAMILY HISTORY
Screening recommendations for patients at increased risk for colorectal cancer because of family history are described in Table 2.
Family history of colon cancer or adenomatous polyp. Recommend screening for patients with 1 first- degree relative or 2 second-degree relatives with a history of colon cancer. Begin screening at either age 40 years or 10 years earlier than the youngest family diagnosis (whichever comes first), and repeat every 5 years.
Familial adenomatous polyposis. Recommend an annual sigmoidoscopy for patients at risk for familial adenomatous polyposis (FAP) beginning at age 10 to 12 years. Advise genetic testing and counseling for families of patients with FAP.
Hereditary nonpolyposis colorectal cancer. Recommend a colo- noscopy every 1 to 2 years for those patients who, based on a genetic or clinical diagnosis, are at increased risk for HNPCC. Begin screening at age 20 to 25 years, or 10 years earlier than the youngest family diagnosis (whichever comes first).
PATIENTS AT INCREASED RISK FROM PERSONAL HISTORY
Personal history of adenomatous polyps. Manage patients with a personal history of 1 or more adenomatous polyps based on the results of their colonoscopy. A follow-up colo- noscopy (scheduled at a time interval determined by clinical judgment) is recommended for patients who have numerous adenomas, malignant adenoma (with invasive cancer), large sessile adenoma, or an incomplete colonoscopy. Patients with advanced or multiple (3 or more) adenomas require follow-up in 3 years; those with 1 or 2 small (less than 1 cm) tubular adenomas, 5 years.
Personal history of colorectal cancer. A colonoscopy at the time of the initial diagnosis is recommended to rule out multiple locations of colon cancer before curative resection surgery. For patients with a preoperative obstruction, a colonoscopy is advised about 6 months following surgery. If the test is normal, routine screening by colonoscopy should resume 3 years postoperatively and every 5 years thereafter.
Personal history of inflammatory bowel disease. Long-standing inflammatory bowel disease (ulcerative colitis or Crohn colitis) increases the risk of colorectal cancer. Recommend an annual or biennial colonoscopy with biopsy after 8 to 10 years of disease for the dual purpose of colorectal cancer screening and management of disease activity.
Virtual colonoscopy. This noninvasive test yields 3-dimensional high-resolution images of the colon. However, patients are exposed to radiation during the procedure and experience discomfort from standard bowel cleansing and air insufflation. Improvements in technology, full understanding of costs, and research into the benefits for patients at average risk are necessary before this test can be implemented as a screening choice.
Altered DNA in stool. DNA can be recovered from stool and tested for genetic abnormalities that cause cancer or various other conditions. Initial studies of this test are promising, and more trials in persons at average risk for colorectal cancer are currently under way.