I spend a lot of time trying to convince my patients to get screened for colorectal cancer. Somehow pap smears , mammograms, blood tests, urine tests and yes the occasional CT or even MRI scan seem doable and require little preparation (at least physiologically). But at the mention of a colonoscopy there is a reticence that seems universal. (After I write this I have to check to see if I am due for mine.) The New England Journal of Medicine presented a “Clinical Practice” article in its September 17th, 2009 issue. Since most of you don’t include this journal in your regular subscriptions (although it is currently available on Kindle) I though that it was a good time to go over the reasons for and methods available to screen for colorectal cancer.
Colorectal cancer is the second leading cause of cancer death in the United States. There will be approximately 147,000 newly diagnosed cases of colorectal cancer and 50,000 deaths from this disease in 2009. There is a gender difference and in women it is the third leading cause of cancer death, after lung cancer and breast cancer. The fact that it comes in third should in no way diminish our concern…remember very few men develop breast cancer. And if you wait for symptoms to occur, it may be too late to affect a cure….in many cases this disease strikes women who have no changes in their bowel habits!
Some of us may be at higher risk than others: If you have a first degree relative who had colorectal cancer before the age of 50 you may have an inborn genetic mutation that will predetermine a high risk for this cancer. There are gene tests (done as blood tests) that can ascertain if you have inherited colorectal cancer syndrome. If you are positive for these specific mutations, you will need very intense screening and perhaps surgery. If a first degree relative had this cancer at 50 years of age or older your lifetime risk doubles and screening should be started at 40 or 10 years younger than the age that your family member was diagnosed with this cancer. And if you have a history of chronic ulcerative colitis or colitis due to Crohn’s disease your risk increases and you should begin surveillance with colonoscopy 8 to 10 years after you received the diagnosis.
So now that we have established that colorectal cancer, like breast and cervical cancer requires screening; what are the stats on the success of the various methods? Let’s start with the “easiest”, the stool tests for occult (not visible to the naked eye) blood. Its advantage is that it can be done in the privacy of your home bathroom. There are 2 types of tests, the first requires 3 stool samples and is not specific for human hemoglobin. (You need to abstain from various foods , especially red meat). The second type may require just one annual stool sample. It specifically tests for human hemoglobin. If either test is positive, you will need follow up with a colonoscopy, to see what is there (causing the minute bleeding), and if necessary, a biopsy of a polyp or lesion to ascertain if it is cancerous or precancerous.. Persons with positive occult- blood tests have a risk of cancer that is 3 to 4 times higher than those with negative tests. The combination of annual stool test followed by colonoscopy probably picks up 50 to 75% of cancers…but there is no guarantee that these cancers are found at an early stage. Indeed if an advanced polyp that is destined to become cancer is present, the stool test for blood may be negative 50 to 80% of the time. What I found interesting from a public health cost perspective (which will be factored into health care reform) is that the expense of screening with annual fecal blood tests, reminder systems and colonoscopy in patients with positive tests is just as costly as screening with colonoscopy!
There is a new stool test that may turn out to be more accurate than the one for occult blood. It detects specific DNA mutations from cancer cells excreted in the stool. The test is expensive and right now researchers don’t know how frequently it should be performed. They also are not sure about the sensitivity of this test, i.e. whether it will pick up advanced, potentially precancerous adenomas.
Barium enema has been found to be inadequate for diagnosing precancerous lesions and is now rarely used for screening.
Now we come to the controversy surrounding CT imaging of the bowel. It, like colonoscopy requires complete bowel preparation (clear liquids for at least 24 hours, ingesting those diarrhea inducing solutions or pills and an evening spent near and on the toilet). Studies have shown that expert radiologists can identify 90% of polyps that are 10mm or larger. But 14% of the time the “polyps” that they diagnose are not actually there when follow-up colonoscopy is performed (i.e. false positive). There also is a concern that the scan may not find flat polyps that can be cancerous or precancerous. The current estimate is that of all those who have this test, 15 to 25% will be referred for subsequent colonoscopy. (And remember this requires a second, unpleasant bowel prep!). Moreover, CT scan frequently does not demonstrate a polyp that is less than 6mm. At this diameter the polyp usually is not cancerous. However small can grow to large and the method of follow-up for small polyps presents a dilemma.
The radiation involved with these scans should also be factored in. Each scan may be fairly low dose, but if done repeatedly or other CT scans are done for other reasons, cumulative radiation can increase future risk of cancer. And finally, whenever scans are done, a lot of “needles in a haystack” may be found, often requiring invasive but ultimately unnecessary interventions. Up to 69% of persons who undergo screening with CT colon scans have at least one finding outside the colon. Studies show that further evaluation is performed in 5 to 16 % of persons who undergo this CT screening.
By now most of you realize that looking at just the lower portion of the colon with sigmoidoscopy is like doing a mammogram on one breast. This uncomfortable procedure (it requires enemas for preparation, and rectal insufflation with air) misses more than 30% of cancers that are present higher up in the colon…especially in women or patients over the age of 60.
Finally we get to the gold standard for colorectal cancer screening, colonoscopy. If you are screened (and have no known risk) you have a 0.5 to 1% chance of having colon cancer found with this test and a 5 to 10% chance of detection of advanced polyps that could become cancer and which can be removed at the time of the screening procedure.. This represents a huge (when in comes to cancer) window of opportunity to diagnose an impending “this can be bad” lesion and prevent cancer. Not only has a future disaster been averted, you are now classified as a polyp “grower” and you and your doctor know that you need to be followed with frequent screening.
As with any test, nothing is perfect. According to the New England Journal review article 2 to 12% of lesions that are 10 mm or larger in diameter may be missed during a colonoscopy. In order for the exam to be complete all the polyps that are seen should be removed. And “when colonoscopy is performed by properly trained endoscopists the risk of serious adverse events is 3 to 5 events per 1000 colonoscopies.” (This includes perforations and bleeding).
Colonoscopy affects every program because it is the last and most effective way to ensure that colorectal cancer is neither present nor impending. Guidelines from the American College of Gastroenterology recommend colonoscopy as the preferred screening test. If one or more polyps are found (which, if we include small polyps, occurs in 20 to 50% of patients), the interval for repeat colonoscopy varies according to the pathologic findings (usually between 1 and 5 years). I f no polyps are present and there are no risk factors, the colonoscopy can be repeated every 10 years.
There are two addendums to what I have just written. It appears that both black men and women develop polyps and colon cancer at a younger age and have a higher mortality from colorectal cancer than white individuals. So the current recommendation by The American College of Gastroenterology is to initiate screening in African Americans at the age of 45. And finally since even colonoscopy can miss the occasional polyp and recent studies show have shown that precancerous polyps can develop in less than 10 years, many gastroenterologists prefer to repeat colonoscopy every 7 years.
Well, this has certainly been a lengthy review. But after reading it I hope you don’t give your doctor or me that look of “you-must-be-kidding:” when we suggest you are due for your colonoscopy. The colon you save may be your own!