Crack in Colon Cancer Screening

Colorectal cancer is the second commonest cancer in North America. Approximately 150,000 new cases occur in the United States and Canada, resulting in about 60,000 deaths per year. Over 70% of these are due to colon cancers. The specific screening tests include colonoscopy and barium enema. Unfortunately, there are flaws associated with these tests.

SPECIFIC SCREENING TESTS OF COLON CANCER

1. COLONOSCOPY:
This is also known as Optical Colonoscopy. It is generally believed to be the most accurate test for diagnosing colon cancer and its potential precursor (polyp). However, this has never been authenticated. Indeed, a recent study reported a false negative rate of 33% in the left colon and 99% in the right colon (Ann Intern Med. 2009;150:1-8). Several other studies affirmed that the false negative rate is about twice as high in the right colon than in the left colon and called attention to the need of a supplementary test for the right colon (JAMA 2006;296(20):2436-2437, Endoscopy. 2003;35:506-10, Gatroenterology. 2004;127:452-6, Clin Gatroenterol Hepatol. 2006;4:1259-64, Gastroenterology. 2007;132:96-102). Other studies also reported false negative rates for polyps in the entire colon to be 22 to 26% (Am J Gastroenterol. 2006;101(2):343-50, Endoscopy. 2008;40(4)284-90).

2. BARIUM ENEMA:
There are 3 distinct varieties of barium enemas:

- Single Contrast Barium Enema - This is the oldest workable exam of colon cancer. It is very easy to perform. "Barium" (barium sulphate and water) is introduced into the colon rectally using hydrostatic pressure until the cecum is distended. Colon cancers tend to stand out on the x-ray films. However, polyps are poorly or not shown at all. In the early 1970’s, it was found that a certain kind of polyp develops into cancer if left untreated. Consequently this technique is no longer used in adult patients, except in those who are gravely ill or are suspected to have colonic obstruction.

- Double Contrast Barium Enema - Since the mid 1970’s, this technique has become very popular in almost every establishment. It is a little tricky to perform but the technique is not difficult to master. The appropriate amount and the correct proportion of barium and air have to be delivered to the entire colon. Cancers/polyps are usually, although not always, captured on film. However, perceiving the cancer/polyp can be difficult. The false negative rate was reported as 10 - 12% by numerous centers.

- Mayo Clinic Barium Enema - This is also known as Fluoroscopic Barium Enema. The technique was published in the early 1980’s. It is quite simple albeit tedious. It consists of attempts to compress every inch of the barium-filled colon with pressures ranging from very low to very high at stages when that segment is slightly, moderately and fully distended. The diagnosis depends on seeing the cancer/polyp on fluoroscopy. Filming is mainly for documentation. The false negative rate was reported by one study as similar to the double contrast barium enema (AJR 1983;140:1143-1149) and by another as 6% (AJR 1983;141:1279-1281). This technique is virtually unknown outside of the Mayo Clinic and Mayo Foundation.

3. CT COLONOGRAPHY:
This is also known as Virtual Colonoscopy. After the introduction of air into the colon, a CT scan of the abdomen is obtained. A 3-D image of the colon is reconstructed with the aid of a computer. The false negative rate has not been firmly established but is generally believed to be similar to that of optical colonoscopy.

CURRENT PRACTICE

If the clinical findings warrant an imaging study of your colon, your doctor will recommend a colonoscopy or, less likely, a CT colonography or a double contrast barium enema. If the result of your test comes back as negative (normal), you are unwittingly facing a false negative rate of at least 22% in the case of a colonoscopy/colonography and a false negative rate of at least 10% for a double contrast barium enema. This is the best Medicine can offer at this time.

SHRINKING THE CRACK

Any adult who has a negative colonoscopy/colonography or double contrast barium enema may simply supplement it with a Fecal Occult Blood Home Test. It should be done 24 months after the negative imaging exam and every 24 months thereafter. However, an adult with a family history of colon cancer or over 50 years of age, should perform the home test after 12 months and annually thereafter. The home test kits can be purchased from almost any pharmacy (in British Columbia, the kits are only available online). The test is totally risk free and the cost of the kits ranges from $9 to $59 each. Be sure to follow the instructions very carefully. If your fecal occult blood test is positive, talk to your doctor to have a follow-up colonoscopy/colonography or double contrast barium enema. This reduces the false negative rate to 1.0 - 4.8%. No test in Medicine has a false negative rate of 0%.

COLON EXAMS IN THE FUTURE
Before speculating on future examinations, I’d like to make several introductory comments:

There are at least 6 reasons why the Mayo Clinic barium enema is not widely used. 1. Superficially, it is very similar to the obsolete single contrast barium enema. 2. It is very tedious to perform. 3. The technique has not been vigorously promoted. 4. Few radiologists find it inviting. 5. Referring doctors do not have the chance to witness the marvel of seeing a cancer/polyp seemingly pops out of nowhere on fluoroscopy. 6. An explanation of why/how it works has never been successfully articulated. (I will try, if I receive a request to do so.) However, I am thoroughly convinced that this method is just as good as stated in the 1983(141) AJR (American Journal of Roentgenology) report. After 25 years of devout execution and evaluation of the Mayo Clinic barium enema, I can confidently say it is the best imaging test of the right colon at the present time and will remain so in the near future.

- 1985 - I performed a double contrast barium enema (as requested) on a well-respected surgeon in our hospital. I did not find anything wrong. While reviewing the films with him, he mentioned that he had iron deficiency anemia and his colonoscopy was negative 12 months earlier. I convinced him to have another exam, a Mayo Clinic barium enema, in our office where the red tapes are fewer and shorter than in the public hospitals. I found a 2.2-cm cancer on the posterior wall of his cecum. He underwent a right hemicolectomy. Cancer cells were present in the lymph nodes and he died of metastatic colon cancer in about 18 months.

- 1997 - During an academic debate with a gastroenterologist, I asserted that the Mayo Clinic barium enema is superior to the double contrast barium enema and colonoscopy. He strongly disagreed. I handed him a signed written statement: For each colon [cancer/]polyp of 0.6 cm or larger I missed on x-rays from January 1 through December 31, 1997, I would donate $100 to the hospital foundation for the exclusive use of the Gastroenterology Section. In that period, I performed approximately 300 barium enemas - about 250 Mayo Clinic and 50 double contrast - and issued about 260 negative reports. Up to December 31, 2002 - my last day working at that hospital - he failed to find any colon cancer/polyp that I had missed from January 1 through December 31, 1997.

NEAR FUTURE
In the near future, colonoscopy will, should the Good Lord willing, be performed in tandem with a Mayo Clinic barium enema. The Achilles heel of colonoscopy is the right colon. The right colon is easily accessible to compression, and thus makes the Mayo Clinic barium enema an ideal companion examination, especially if a pneumatic paddle instead of a lead glove (the 1983 compression device) is used for the vigorous and meticulous compression. This combination can reduce the false negative rate for the entire colon to 1.3% or possibly even lower. This is as close to perfection as any medical test can get! A false negative rate of 15%, namely a sensitivity of 85% with a similar or higher specificity, is currently deemed satisfactory for screening tests.

DISTANT FUTURE
In the distant future, hopefully not too distant, CT colonography or MRI colonography alone may suffice for screening purposes if a suitable gas, liquid, foam, gel, cream or mixture can be found to temporarily halt the peristalsis and optimally distend the colon during the CT or MRI scan.

SUGGESTION:
Please copy-and-paste the URL of this article (below) to an e-mail and send it to your friends and relatives who have a family history of colon cancer and, perhaps, to your colonoscopist as well.
http://www.buzzle.com/articles/crack-in-colon-cancer-screening.html