USPSTF on colon cancer: “The best screening test is the one that gets done”

The large intestine—the colon and rectum—is about the last five feet of the human digestive tract. Under normal circumstances, the cells that line the colon have mercurial little lives, and are replaced every five to seven days.

But sometimes these cells develop mutations—DNA errors caused by chance, genetics, or environmental carcinogens—and then they become dysfunctional, forming little knuckles of tissue called polyps

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In a small minority of cases, the banged up cells that grew into a polyp suffer additional mutations and turn cancerous. Thankfully the malignant conversion process is typically a slow one, perhaps as long as 10 years. So if we can remove a polyp before cancer develops, we can do a little cancer-victory dance.

And when it comes to colorectal cancer, we could use a little more dancing. It’s the second leading cause of cancer deaths here in the U.S., mostly because we find it too late. More than 50% of newly diagnosed patients have stage III and IV cancer, where the cancer has spread outside the colon, making it much more difficult to cure. 5-year survival rates for stage III and IV disease are approximately 65% and 10%, respectively. That’s the Chicken Dance when we want to be doing Gangnam Style… or something.

The United States Preventive Services Task Force (USPSTF) recently re-evaluated its recommendations for colon cancer screening. Citing the fact that nearly a third of eligible Americans have not been screened, the task force took a very pragmatic approach, stating “the best screening test is the one that gets done.”

The USPSTF found that four screening strategies provided a comparable balance of risk and benefits, and life-years gained. So take your pick.

  • Colonoscopy every 10 years: colonoscopy is the best way to find (and remove) colon polyps, but it’s also the most invasive and risky. The pre-procedure blow-out prep feels to many like it could be an Olympic event (the Russians would cheat, somehow), and the procedure itself carries a small but serious risk of perforating the colon (4 out of 10,000 procedures). If a polyp is removed during the procedure, there is a small risk of major bleeding (8 of every 10,000 procedures). 
  • Annual fecal immunochemical testing (FIT): this is a relatively new, new-and-improved way to look for blood in the stool. Older forms of stool blood tests could be tricked by certain dietary items like meat, or by blood from somewhere else in the GI tract--from an ulcer for example. But FIT is not so easily fooled.
  • Flexible sigmoidoscopy every 10 years, with annual FIT: sigmoidoscopy examines just the last third of the colon, where most colon cancers are found. It’s easier to prepare for and is a lower risk procedure than a colonoscopy.
  • CT colonography every 5 years: because this test sees everything in one’s abdomen, not just the colon, the USPSTF notes that 40-70% (which one is it?!) of screening CT colonography exams identify incidental anatomical findings outside the colon. Typically these don't end up being anything serious; but you don’t know that until you’ve proven it, so more testing is often required. Radiation exposure from the test has been raised as a concern, but the test typically uses around 7 mSv of radiation, and the average background radiation here in the U.S. is about 3 mSv.

It might be obvious, but a positive FIT, flexible sigmoidoscopy, or CT scan typically leads to a colonoscopy, which why advocates of colonoscopy point out that it’s not just a screening test: it can be a treatment too.

The USPSTF recommends screening for average-risk people ages 50-75, and maybe for someone in the 76-85 range who has never been screened. It’s diminishing returns after age 75 because, given the fact that it takes a polyp around a decade to become cancerous, people of that age are more likely to die from something else. And the risks—a perforation or bleeding during colonoscopy, or an Olympic-caliber face plant as one rises from the toilet for the seventeenth time during the prep—increase with age.

One additional risk with colonoscopy is that it includes light anesthesia, which carries a small risk of causing heart or respiratory problems. Many colonoscopies are now being performed with an intra-venous infusion of a sedative called propofol, but when I had my inaugural colonoscopy last year, I was given fentanyl, a narcotic; and midazolam, a sedative that provides amnesia. This “cocktail” provides what suffering humans often search for: something for the pain, and something for the memories.

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