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Effect of Colonoscopy Screening on Risks of Colorectal Cancer and Related Death

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Re: Effect of Colonoscopy Screening on Risks of Colorectal Cancer and Related Death

#11

Post by JamesBarney »

groceryheist wrote: post #5

Sensationalist title to a good news story: there was no intent-to-treat effect, but a low conversion rate. The ETT is a pretty impressive 50% mortality reduction. Also study is limited by a short 10 year follow-up period but there will be a 15 year follow up. So I'll still get my colonoscopy, thanks

When everyone invited for a colonoscopy is compared to the control group 42% showed up and got a colonoscopy 18% fewer people got colon cancer same number of people died of colon cancer

When everyone who got a colonoscopy is compared to the control group 30% fewer got colon cancer 50% fewer people died of colon cancer

This data makes me think the mortality reduction benefit is bogus, but the cancer prevention benefit is real, and probably greater than 18%, maybe closer to 36-40%. If the colon cancer mortality benefit was real you'd see some reduction in the intention to treat group, and it'd be smaller than the cancer prevention effect. (The most aggressive cancers tend to be harder cancers to catch in time because they most so quickly, so most cancer screening tests will prevent more cancers than deaths)

Re: Effect of Colonoscopy Screening on Risks of Colorectal Cancer and Related Death

#12

Post by cies »

Many years ago I learned about Japanese doctor Shinya. He pioneered the colonoscopy an found that diet was a big factor in intestinal health.

Here some videos (may be NSFW):

https://www.youtube.com/watch?v=B1LREA1ZuUE

But there are lots more to see.

I believe what he discovered is important. Not that I believe his advice to drink ionized water (Kangen water) is scientifically sound. But that does not matter for the discovery that switching to eat rice and veggies cleans your intestine.

Re: Effect of Colonoscopy Screening on Risks of Colorectal Cancer and Related Death

#13

Post by akvadrako »

bryan0 wrote: post #6
hannob wrote: post #4

Earlier quoted context omitted.

They're doing an intention to treat analysis, which can be a bit confusing, but statistically makes sense and is the gold standard for clinical trials. You're basicall saying "our randomization at the beginning of the trial is key to avoid biases, so we can't reassign people from the treatment group to the other group, even if they practically don't get the treatment". The reason is if you allow people to switch, you…

Thanks. That explanation on avoiding selection bias makes sense, but it seems like the study is saying those who choose to get a colonoscopy (whether invited or not) are 50% less likely to die of colon cancer. Also I’m not sure if the article mentioned this, but the data seems to imply that the % of people who opted to get a colonoscopy was similar in the invited and control group.

That suggests something strange though – that those who were invited but non-tested were more likely to die of colon cancer than non-invitie non-testers.

Re: Effect of Colonoscopy Screening on Risks of Colorectal Cancer and Related Death

#14

Post by Someone »

tylermenezes wrote: post #9
rippercushions wrote: post #7

Earlier quoted context omitted.

Where are you getting "50% mortality reduction" from? The article says the reduction was zero: > After 10 years, the researchers found that the participants who were invited to colonoscopy had an 18% reduction in colon cancer risk but were no less likely to die from colon cancer than those who were never invited to screening.

> When the investigators compared just the 42% of participants in the invited group who actually showed up for a colonoscopy to the control group, they saw about a 30% reduction in colon cancer risk and a 50% reduction in colon cancer death

I don’t see how that says much about the usefulness of colonoscopy.

The people in the treatment group who didn’t show up must have had a 36% increase in colon cancer death (not explicitly stated in the article, but can be derived from the numbers. You need 42% × 50% + 58% × ? = 1), and (solving 42% × 70% + 58% × ? = 1) a 21% increase in colon cancer risk.

Something must have made them different from the control group. Maybe, they didn’t show up because they already were being treated for colon cancer?

Re: Effect of Colonoscopy Screening on Risks of Colorectal Cancer and Related Death

#15

Post by pbourke »

JamesBarney wrote: post #8
bryan0 wrote: post #3

> When the investigators compared just the 42% of participants in the invited group who actually showed up for a colonoscopy to the control group, they saw about a 30% reduction in colon cancer risk and a 50% reduction in colon cancer death. I’m really confused by this data. First of all, are they testing the efficacy of colonoscopy or the efficacy of inviting people to colonoscopy? And then how is the former group’s…

The gold standard is the invitation. Imagine a study where you try to get one group of people to exercise, and you leave the other alone as a control group. Imagine you find that everyone who actually does the exercise lives much longer. This might be due to the exercise, or it could be that exercise doesn't work but healthier more responsible people followed through with the exercise. And the being healthier and mor…

In this case they are examining colon cancer and deaths from it, and the colonoscopy is a diagnostic test for colon cancer. I feel that the results are being presented to the public in a very misleading way. People will read this headline and conclude that they don’t need to get a colonoscopy which I don’t think follows from this study at all.

Re: Effect of Colonoscopy Screening on Risks of Colorectal Cancer and Related Death

#16

Post by zerocrates »

akvadrako wrote: post #13
bryan0 wrote: post #6

Earlier quoted context omitted.

Thanks. That explanation on avoiding selection bias makes sense, but it seems like the study is saying those who choose to get a colonoscopy (whether invited or not) are 50% less likely to die of colon cancer. Also I’m not sure if the article mentioned this, but the data seems to imply that the % of people who opted to get a colonoscopy was similar in the invited and control group.

That suggests something strange though – that those who were invited but non-tested were more likely to die of colon cancer than non-invitie non-testers.

I suppose that by refusing to get a colonoscopy even when specifically prompted to do so, you're maybe sorting yourself into a more "unhealthy" group than the general population of non-colonoscopy-havers.

Re: Effect of Colonoscopy Screening on Risks of Colorectal Cancer and Related Death

#17

Post by [deleted] »

pbourke wrote: post #15
JamesBarney wrote: post #8

Earlier quoted context omitted.

The gold standard is the invitation. Imagine a study where you try to get one group of people to exercise, and you leave the other alone as a control group. Imagine you find that everyone who actually does the exercise lives much longer. This might be due to the exercise, or it could be that exercise doesn't work but healthier more responsible people followed through with the exercise. And the being healthier and mor…

In this case they are examining colon cancer and deaths from it, and the colonoscopy is a diagnostic test for colon cancer. I feel that the results are being presented to the public in a very misleading way. People will read this headline and conclude that they don’t need to get a colonoscopy which I don’t think follows from this study at all.

[deleted]

Re: Effect of Colonoscopy Screening on Risks of Colorectal Cancer and Related Death

#18

Post by rob74 »

JamesBarney wrote: post #8
bryan0 wrote: post #3

> When the investigators compared just the 42% of participants in the invited group who actually showed up for a colonoscopy to the control group, they saw about a 30% reduction in colon cancer risk and a 50% reduction in colon cancer death. I’m really confused by this data. First of all, are they testing the efficacy of colonoscopy or the efficacy of inviting people to colonoscopy? And then how is the former group’s…

The gold standard is the invitation. Imagine a study where you try to get one group of people to exercise, and you leave the other alone as a control group. Imagine you find that everyone who actually does the exercise lives much longer. This might be due to the exercise, or it could be that exercise doesn't work but healthier more responsible people followed through with the exercise. And the being healthier and mor…

Or it could be that the people that are not necessarily healthier, but have a history of cancer in their family, may be more likely to respond to a colonoscopy invitation? One way or the other, this is all just guesswork...

Re: Effect of Colonoscopy Screening on Risks of Colorectal Cancer and Related Death

#20

Post by JamesBarney »

pbourke wrote: post #15
JamesBarney wrote: post #8

Earlier quoted context omitted.

The gold standard is the invitation. Imagine a study where you try to get one group of people to exercise, and you leave the other alone as a control group. Imagine you find that everyone who actually does the exercise lives much longer. This might be due to the exercise, or it could be that exercise doesn't work but healthier more responsible people followed through with the exercise. And the being healthier and mor…

In this case they are examining colon cancer and deaths from it, and the colonoscopy is a diagnostic test for colon cancer. I feel that the results are being presented to the public in a very misleading way. People will read this headline and conclude that they don’t need to get a colonoscopy which I don’t think follows from this study at all.

The study results are "colonoscopies do not lead to a reduction in colon cancer mortality". Reporting that isn't misleading that's what the study says.

Basically in the treated group of 1103 of every 10,000 people died. And in the control group 1104 of every 10,000 people died.

So to summarize the study. Inviting someone to a colonoscopy reduces their risk of getting colon cancer by 22 basis points. Their risk of dying from colon cancer by 3 basis points, and their risk of dying of any cause by 1 basis point.

With the actual risk reduction being up to 5x this assuming it's a 20% difference in the rate of getting colonoscopies which is driving the difference.

But this makes metformin look good because it drives a much larger overall reduction in risk.

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