An invitation to a screening
Dr. Wilson: This was a bit of an interesting trial design. I think I’m correct, Dr Lin, that this was the first randomized trial of screening colonoscopy. But they didn’t really randomize people to get a colonoscopy versus not get a colonoscopy. Can you tell us why this differed from that study design, which I’d have thought would be simpler way of assessing this?
Dr. Lin: It’s definitely an important point to highlight about the study. What investigators did was randomize patients to receive an invitation to get a screening colonoscopy. When the trial was set up, they randomized people before they were asked whether they wanted to participate in the study. If you did it the other way around, by first asking them whether they wanted to be in the study and then randomizing them, you would have been assured that more of them probably would have gotten the colonoscopy.
But in this case, they were more interested in figuring out the real-life results of having a national program that invited patients to receive screening colonoscopy. Because we know that everyone that you recommend to get a colonoscopy doesn’t necessarily want to do that, forgets to do it, or something happens that prevents their actually getting it.
When it comes to measuring the effectiveness of the colonoscopy, it perhaps wasn’t the greatest type of study to do that. But I think it did provide some information about what would happen if you invited people to get colonoscopy, in terms of how many would do it and the results overall for that population.
Lower participation numbers than expected
Dr. Wilson: Dr. Johnson, the data show that 42% of people who were in that invitation arm followed through and got their colonoscopy. You’re a gastroenterologist. Does that seem low or about right? Do about half of people who should get a colonoscopy end up getting one?
Dr. Johnson: No, it’s low. In the United States, those numbers are probably in the 70% range. Certainly, the test doesn’t work for people who don’t get the test performed. So, if 42% of those randomized to receive an invitation to get the colonoscopy got one, that really means the majority of patients never got the test.
Dr. Wilson: Certainly, we wouldn’t expect impressive results if they don’t get the test. But on the other hand, I imagine that people who choose to get the test when they’re invited are sort of a different breed. Perhaps they’re more health conscious or living in other healthy ways. Is that something we should worry about when we look at these results?
Dr. Johnson: I don’t think you can stratify based on this study. Factors like ethnicities and diet weren’t really explained. The key element that will hopefully have the major take-home impact is quality. It’s not just the test. It’s how the test is done.
The key results
Dr. Wilson: Let’s start with the big picture. This was a study looking at everyone invited; not the subgroup of people who got the colonoscopy, but the real randomized study population.
Dr. Lin, the study did show that the invited group had a lower risk of colon cancer over the next 10 years. That’s a good thing, I imagine.
Dr. Lin: I think that’s a significant benefit. Initially in the first few years, they had more colon cancers diagnosed. But that’s probably because those were cancers that were already existing and couldn’t be prevented by the test.
But then over the years the curves crossed, and by the end of the average follow-up of 10 years, there was a significantly lower rate of colon cancers being detected. That’s as you would expect, because you’re finding polyps and removing them before they became colon cancer.
Dr. Wilson: Dr. Johnson, is that the natural history of colon cancer? It starts out as a polyp that maybe can be easily removed and doesn’t require more therapy. Is that why screening colonoscopy is helpful?
Dr. Johnson: The ultimate goal of screening is prevention of cancer, rather than detection of cancer. That occurs by identification and complete removal of the polyps that we find that are precancerous. The key is, first, detection, and second, resection. Adequate resection comes down to some very significant issues of quality, which are questions that I’d raised about this study, and we can talk about momentarily.
Dr. Wilson: Absolutely. Let me first go through the two other big findings in this study.
The fact that there were fewer cases of colon cancer over 10 years seems good. But colon cancer mortality was not significantly different in the two groups. Now, of course, we know that not everyone got a colonoscopy. I would have expected though, if you had less colon cancer, you’d have less death from colon cancer.
Dr. Lin, what might explain this disconnect?
Dr. Lin: I think there are a couple of possible explanations.
One explanation is that they just didn’t follow the people long enough. Colon cancer takes a long time to go from an adenoma to cancer, and from cancer to something that would cause the patient’s death. You may need to follow them for longer than the 10 years that most of these patients were followed to see that benefit. I think there probably will be benefit after a while, because if you are removing colon cancers that otherwise would have progressed and metastasized, you often see a benefit.
We also have to consider the other possibility that not all the polyps removed necessarily were going to progress to advanced cancer. Therefore, you weren’t seeing the death benefit because not every polyp that was removed was necessarily going to cause health consequences.