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Episode 78: A 47-Year-Old who Comes in Asking About Colon Cancer Screening
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Episode 78: A 47-Year-Old who Comes in Asking About Colon Cancer Screening
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T00H07M19S
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2022-02-28T00:00:00.0000000
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Language: EN.
Segment:0 .
[upbeat intro music] [Dr. Handy] Hi, welcome to Harrison's Podclass, where we discuss important concepts in internal medicine. I'm Cathy Handy. [Dr. Wiener] And I'm Charlie Wiener, and we're coming to you from the Johns Hopkins School of Medicine. [Dr. Handy] Welcome to today's episode, a 47-year-old who comes in asking about colon cancer screening. [Dr. Wiener] Okay, so Cathy, you'll like this one.
A 47-year-old woman saw a television show advocating for screening colonoscopy to prevent colon cancer, and she wishes to undergo the procedure. She has no family history of colon cancer and currently has no symptoms referable to the GI tract. The question's going to ask, which of the following statements is true about colonoscopy as a screening test for colon cancer? Option A. colonoscopy remains the gold standard for imaging the colonic mucosa; option B. CT colonography has replaced traditional colonoscopy for many younger patients because of its ability to detect serrated polyps with greater sensitivity; option C is flexible sigmoidoscopy would be as effective as colonoscopy for detecting colon cancer in this patient; option D. she should not start colon cancer screening until she's over 50 years old; and option E. stool hemoglobin and DNA tests are more sensitive than colonoscopy.
[Dr. Handy] All right, there's a lot to unpack here, and recommendations are changing quickly. So let's start by saying that colon cancer is the third leading cause of cancer death in the U.S. for men and women, so an important consideration for physicians. Screening has been shown to be effective in reducing mortality. As we've talked about a few times for other disorders, there are disparities in mortality in the United States.
Black Americans have a higher incidence and are more likely to die from colon cancer compared to other races. [Dr. Wiener] When we talk about screening, what are we really looking for? [Dr. Handy] Like all cancer screening, the core principle is that detecting early or precancerous lesions will prevent the development of advanced disease. Adenocarcinoma of the colon develops from precancerous colonic polyps, and most screening strategies rely on detecting these early lesions, although newer techniques rely on detecting either small amounts of blood in the stool or abnormal DNA suggesting precancerous lesions.
[Dr. Wiener] Okay, well, let's go through the options here, starting with age. Option D says she should not start screening until she's over 50 years old. Is that true? [Dr. Handy] Well, if we'd been discussing this in prior years, that would be a true statement, however, just last year, the U.S. Preventive Services Task Force lowered the starting age for colon cancer screening in average risk individuals from 50 years of age down to 45 years of age.
This recommendation comes from evolving science that while most colon cancers present in patients over 60 years old, there are a greater number presenting at younger ages and that screening may be effective. [Dr. Wiener] You mentioned average risk. Who is or who is not average risk? [Dr. Handy] Good point. So average risk implies no symptoms, no first degree family history of colon cancer, no inflammatory bowel disease and no history of polyps.
If an individual has any of those, then they would be considered to be at higher than average risk, and there are different recommendations for them. [Dr. Wiener] Okay, back to our question, it asked which statement is true. We already ruled out D. because the recommended age for screening is 45, not 50. Which is the correct answer then?
[Dr. Handy] The correct answer is A. colonoscopy remains the gold standard for examining the colonic mucosa for polyps. And this assumes that the patient has a good bowel preparation, and the examination goes to the cecum. [Dr. Wiener] How often should it be done? [Dr. Handy] If a patient has a negative colonoscopy, the recommendation is to repeat it in 10 years.
Now obviously, if abnormalities are found, biopsies can be done, or if polyps are found, then they can be removed, and the patient will have more frequent colonoscopies. [Dr. Wiener] Option B mentioned CT colonoscopy, or so-called virtual colonoscopy. [Dr. Handy] Yeah, that's using barium and a high-resolution CT scan to essentially develop a virtual view of the inside of the colon.
Now while that does have a high sensitivity for detecting polyps, it is not as sensitive as a well-prepped colonoscopy, particularly in the presence of flat or serrated polyps. And colonoscopy has the advantage of being diagnostic and therapeutic, because you can remove the polyps if you find any. [Dr. Wiener] Option C mentions flexible sigmoidoscopy. What about that?
[Dr. Handy] The use of sigmoidoscopy was based on the historical finding that the majority of colorectal cancers occurred in the rectum and the left colon, and that patients with right-sided colon cancers also had left-sided polyps. Over the past several decades, however, the distribution of colon cancers has changed in the United States with proportionally fewer rectal and left-sided cancers than in the past.
Large American studies of colonoscopy for screening of average risk individuals show that cancers are roughly equally distributed between the left and right colon, and half of patients with right-sided lesions actually have no polyps in the left colon. So colonoscopy is preferred over sigmoidoscopy. [Dr. Wiener] Okay, well, then let's finish with the stool studies.
I know the guaiac test that I trained with is no longer in use. But what about the newer stool studies, many of which are advertised on TV also? [Dr. Handy] Yeah, so first, guaiac has been replaced by a highly sensitive fecal immunochemical test for hemoglobin that detects occult bleeding, presumably from polyps. While stool tests for occult blood have been shown to decrease mortality rate from colon cancer, they do not detect some cancers and many polyps, and direct visualization of the colon is a more effective screening strategy.
Also, if it's positive, the bleeding can be coming from any place along the GI tract. So a positive result is not specific for a colon source, and a positive test requires a follow-up colonoscopy. If you're using this strategy, the test should be repeated yearly. [Dr. Wiener] Okay, and then what about the stool DNA test? Again, every television show I watch has a commercial for them.
[Dr. Handy] The new stool DNA tests look for genetic mutations and methylation patterns that are associated with polyps and colon cancer. They also test for occult blood. The result is positive or negative based on a complex detection algorithm. Now these tests have been shown to have a high sensitivity and specificity for detecting precancerous polyps and cancers compared to fecal immunochemical tests, which only detect blood.
They do produce more false positives, however. No studies to date have demonstrated that they are superior to colonoscopy in preventing colon cancer death, but more studies are ongoing. Now if utilized, a positive test should be followed with a colonoscopy, and a negative test should be repeated every three years. [Dr. Wiener] Great. Wow, a lot of stuff. The teaching points here are that there are recent changes in colon cancer screening recommendations, so that now average risk patients should start at age 45 instead of age 50.
Colonoscopy is still the gold standard, but stool DNA and occult blood tests every three years are non-invasive and efficacious as a screening strategy. [Dr. Handy] And you can read more about this in Harrison's chapter on endoscopy and colon cancer, plus the U.S. Preventive Services Task Force recommendations are online at uspreventivetaskforce.org. [outro music] [Mr. Shanahan] This is Jim Shanahan, publisher at McGraw Hill.
Harrison's Podclass is brought to you by McGraw Hill's Access Medicine, the online medical resource that delivers the latest trusted content from the best minds in medicine. Go to accessmedicine.com to learn more.