Screening could prevent more than half of colorectal cancer deaths: virtual colonoscopy is gaining traction due to ease of the procedure compared to standard colonoscopy.
But recent study findings show that computerized tomographic (CT) colonography is as effective as traditional colonoscopy at identifying polyps, which may change the public's view of colorectal cancer screening. The CT procedure, virtual colonoscopy, may remove some of the "ick" factor associated with traditional colonoscopy: The procedure is relatively noninvasive and requires no sedation, although it does require traditional "prep"--colonic cleansing using a special laxative.
The study, conducted by Mayo Clinic's Dr. C. Daniel Johnson, chairman of the Radiology Department, closes a chapter on a study published in a 2008 issue of the New England Journal of Medicine (NEJM) that suggested virtual colonoscopy was as good as standard colonoscopy, but did not specifically discuss its effectiveness with older patients, in whom larger polyps tend to occur.
Dr. Johnson analyzed data from the National CT colonography trial used in the initial NEJM study, which involved 2,600 patients, to analyze the performance of virtual colonoscopy in patients over 65 versus those aged 50 to 65. Researchers found no statistical difference in diagnosis between the two procedures. Virtual colonoscopy has now been green lighted for patients over 65. The study was published online February 23, 2012 in the journal Radiology. And a Dutch study published online in The Lancet Oncology in November 2011 found a 50 percent greater participation in screening using virtual colonoscopy compared to standard colonoscopy.
COLORECTAL SCREENING OPTIONS. Standard colonoscopy, in which a long flexible tube with a camera at the tip is slid into the patient's rectum to view the colon, has long been regarded as the gold standard of colorectal screening. If polyps or growths are found during the procedure, the doctor removes them using a wire loop that passes through the tube. But the negatives include possible bleeding, perforation of the intestine, and an adverse reaction to the laxative required for colonic cleansing or the sedative. Hence, the American College of Physicians does not recommend this type of screening for patients over 75, or who have a life expectancy of less than 10 years.
With virtual colonoscopy, carbon dioxide is blown into the colon to inflate it via an enema tip that is minimally inserted into the rectum. The patient then passes through a machine that takes a series of CT images of the large intestine, which are combined to create a three-dimensional view of the entire colon and rectum. The patient still must undergo colon cleansing, but there is no downtime due to sedation after the procedure.
Both procedures search for signs of pre-cancerous growths, polyps, cancer or other diseases in the large intestine. If polyps or growth are detected via virtual colonoscopy, the patient must undergo a conventional colonoscopy to remove them.
With sigmoidoscopy, a flexible tube is inserted only into the lower third of the colon to look for abnormal growths. The entire colon is not examined.
Stool-based screening, which includes an annual guaiac-based fecal occult blood test (gFOBT) and fecal immunochemical test (FIT), can be done at home over several days. They require the patient to collect and store stool samples, which are then taken to a lab for testing.
FIT AND COLONOSCOPY. FIT and standard colonoscopy produced almost identical results in finding cancerous lesions, according to a study published in the February 23, 2012 issue of the NEW that compared one-time colonoscopy in 26,703 subjects age 50 to 69 with FIT every two years in 26,599 participants. The colonoscopy subjects had 30 incidences of colorectal cancer compared to 33 in the FIT group. But colonoscopy proved superior to FIT in identifying advanced adenomas (benign growths): 514 patients in the colonoscopy group compared to 231 participants in the FIT group, and in identifying nonadvanced adenomas: 1,109 in the colonoscopy group versus 119 in the FIT group. Advanced mas are usually considered a marker for colorectal cancer. The 10-year follow-up will be completed by 2021.
REMOVING POLYPS REDUCES MORTALITY RATES BY 53 PERCENT. Further evidence to support the benefits of colorectal cancer screening is found in another study, published in the same issue of NEJM, which reported on long-term prevention of colorectal cancer deaths as a result of polyp removal. Patients were followed for over 23 years. Of 2,602 patients in the study who had adenomas removed, after a median of 15.8 years, 12 died from colorectal cancer compared to 25.4 expected deaths in the general population, a 53 percent reduction in deaths. All the patients in the adenoma cohort had adenomas, including 57.3 percent with advanced adenomas, representing a higher risk group than the general population. The findings provide an indirect estimate of the effect of removing adenomas, considered the primary intervention in screening colonoscopy, researchers said. Meanwhile, long-term, randomized, controlled trials of screening colonoscopy in the general population are underway in northern Europe and Spain, and by the Veterans Administration in the U.S. Results will be available in about 10 years.
BOTTOM LINE. All of the evidence points to the importance of colorectal cancer screening. "The key isn't so much modality; the key is getting screened," said Mayo Clinic's Dr. Johnson.
WHAT YOU SHOULD KNOW The American College of Physicians' new screening guidelines recommend that adults be screened starting at age 50, or, if there is a family history. 10 years earlier than the family mercer who was diagnosed. Other risk factors that need to be taken ink account include race (African-Americans have the highest risk and mortality rate from the disease), and medical issues such as polyps, inflammatory bowel disease or previous colorectal cancer.
S. YOUSUF ZAFAR, MD, MHS, Assistant Professor of Medicine-Division of Medical Oncology, Duke Cancer Care Research Program, Duke Cancer Institute
Standard Colonoscopy Still the Preferred Procedure
"As a gastrointestinal oncologist I treat patients who have been diagnosed with colorectal cancer. Despite the availability of well-studied screening tests for colorectal cancer, in 2012 over 140,000 people will be diagnosed with the disease. A substantial proportion of these cases might be avoided with appropriate colorectal cancer screening. My preference is for colonoscopies. I encourage those at least 50 years old (or younger if certain risk factors are identified) to obtain a screening colonoscopy if possible. Understandably, stool-based screening like fecal occult blood tests are more convenient and less invasive, but existing stool-based tests only detect cancer after it has already developed. A colonoscopy can detect and remove pre-cancerous polyps, and removal of pre-cancerous polyps might save lives. Virtual colonoscopies present an effective and convenient alternative, but not all insurance plans (including Medicare) cover the test."
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|Author:||Zafar, S. Yousuf|
|Publication:||Duke Medicine Health News|
|Date:||May 1, 2012|
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