There’s some very good news about colon cancer. Both incidence and mortality among adults 50 and older have plummeted. Mortality is now less than half of what it was in 1975 and incidence is down almost 40%. You may be thinking it’s because of the big push to get everyone screened—you know, the dreaded colonoscopy that awaits everyone once they turn 50 (sooner if a close relative has had the disease).
In an interesting article titled, “Colorectal Cancer on the Decline—Why Screening Can’t Explain It All,” that appeared in the April 28, 2016 issue of the New England Journal of Medicine, Gilbert Welch, MD, MPH and Douglas Robertson, MD, MPH examine the evidence.
First of all, they point out, none of the trials to determine the impact of colon cancer screening have shown a 50% reduction in mortality. Further, on a population basis, the uptake of screening has been painfully slow—only reaching half the population by 2005. They authors conclude,
“…it’s hard to imagine a substantial screening effect at the population level showing up much before this new millennium started.”
So if we can’t give screening all the credit, what do they think explains the decrease in mortality? They say there are three main contributors:
- Better treatment
- Earlier detection of symptomatic disease (note: this is different from screening asymptomatic people)
- Fewer cancers developing in the first place
Let’s examine each of these.
When I was in training many moons ago, the options were limited. If the disease was caught early before any spread, you could be cured with surgery. If not, your chemotherapy options were very limited and mostly not particularly effective. Now advances in surgery, including the option of resecting individual metastases, as well as the addition of more types of chemotherapy, have reduced longer-term mortality.
Early detection of symptomatic disease
The authors suggest that,
“patients with colorectal cancer symptoms are most likely presenting earlier and being diagnosed earlier than they were in the past”
because of increasing use of endoscopy (sigmoidoscopy and colonoscopy) to evaluate symptoms. The decline in patients initially being seen with metastatic disease supports this assumption.
Fewer cancers in the first place
According to the paper, the overall incidence of colon cancer began to decline “well before the expected effect of polypectomy” (removal of precancerous polyps at the time of screening colonoscopy). Speculating on what could have lead to a decrease in incidence, Welch and Robertson suggest a change in diet (e.g., reduced consumption of smoked and cured meats—bacon, hot dogs, and so forth—could have resulted in a lower exposure to carcinogens, such as nitrosamines). Other potential factors include widespread use of antibiotics that alter the microbiome and drugs (e.g., aspirin, hormone-replacement therapy, and statins) that have known associations with a lower rate of colon cancer.
Why this paper is important
One of the reasons this paper is important is that it points out real progress in reducing a potentially deadly disease requires more than just screening; although, in the case of colon cancer, it certainly is a critical strategy. But other interventions, such as changes in diet, drug use, and improved treatments likely also play important roles. Understanding this should help us keep our perspective and avoid falling into the trap of putting all of our proverbial eggs into the screening basket.