‘Screening’ for colon cancer can PREVENT it
— by removing pre-cancerous growths before they turn into cancers. You’ll be back on your feet the same day, and back at work two days later.
The growths are called polyps. Removing them in time not only stops them from turning cancerous but also relieves any symptoms that they cause.
What symptoms? Most polyps don’t cause any (which is one more reason to screen). Larger ones are more likely to cause symptoms, including blood or mucus in the toilet bowl, changes in bowel habits (constipation or diarrhea or alternating between the two), abdominal pain, or unexplained fatigue.
There are various screening tests. “Which test is best?” is a standard question, to which the standard answer is “The best test is the one that gets done!” The one that removes polyps is called colonoscopy.* At first you will probably be offered a simpler, cheaper test, which will indicate whether a colononscopy is appropriate; but the possibility of removing polyps now (instead of removing bigger bits later!) is the most persuasive reason to get screened.
Yes, screenings also may find early cancers; but a successful screening is one that prevents a cancer, not one that finds a cancer. (You can even have a borderline case in which polyp removal doesn’t technically prevent the cancer, but still removes it before it spreads beyond the polyp!)
At what age should screening begin? The U.S. Preventive Services Task Force has found a “substantial net benefit” from screening for persons aged 50 to 75 years, and a “moderate net benefit” for persons aged 45 to 49, and accordingly makes a “grade-A” recommendation for ages 50 to 75, and a “grade-B” recommendation for ages 45 to 49. The American Cancer Society also recommends screening from age 45. These recommendations are supported by, e.g., research published in 2017, showing that the rise in incidence of colorectal lesions between the 40–44 and 45–49 age brackets is much larger than the rise between the 45–49 and 50–54 brackets.** Screening should start earlier if you have a family history of colon cancer or polyps, or belong to a high-risk ethnic group (e.g. Afro-American or Euro-Jewish), or have a predisposing genetic condition, or have symptoms.
Of course colonoscopy isn’t risk-free. Nothing is. That’s why the usual recommended age for screening is 45 and not (say) 18! It's about managing risk, not eliminating it.
Yes, it’s true that most polyps don’t turn cancerous. But it’s also true that nearly all colon cancers begin as polyps.
Your “absurd presumption” in your own good fortune (as Adam Smith called it) clashes with the notion that you might have colon (bowel) cancer. But it doesn’t clash with the revelation that colon cancer is highly preventable if you’re willing to endure a minor disruption. So that’s what I told you first. And that’s what other promoters of ‘screening’ should be telling you first—on the cover of the brochure, on the outside of the envelope, on the home page of the website, etc. Yes, the benefit of early detection of cancer ought to be persuasive enough. But if you want to persuade people, you need to give them the information that they actually find persuasive—not to be confused with the information that they ought to find persuasive!
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* A sigmoidoscopy may also be able to remove polyps, but only from the lower part of the colon; and if any polyps are found, a follow-up colonoscopy is recommended to see if there are more in the upper part of the colon.
** Some government health services are yet to respond to these findings, still offering tests from age 50, or even 60!
[Updated 12 August 2023.]