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Comment by dgellow | Hacker News Reader

Given people don’t read the full article, and that feels pretty important in this discussion, I will quote the way it ends:

> One thing is clear: Screening works. If you’re of the appropriate age, please get screened. If your tubes are acting funny, please get screened without delay. The best method and the level of benefit are debatable, but we know it helps. Use a stool test if you want (multitarget DNA test if you can), or a colonoscopy, or a sigmoidoscopy, or a “virtual” CT colonoscopy, or a crazy edible camera. Do one of them. Statistics show colorectal cancer is highly curable when caught early, and now that we have feisty checkpoint inhibitor immunotherapies,it’s probably even better now. Just do it. Your tubes will thank you.

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That's unfortunate, because it's a poor summary of the actual paper the article is discussing. If you bother to read the rest of the article, you'll see the actual summary of the trial, and it's pretty darned easy to interpret for yourself:

https://asteriskmag.com/media/pages/issues/04/you-re-invited...

to wit:

> The 18% reduction in colorectal cancer incidence was statistically significant, while the 10% reduction in colorectal cancer mortality and 1% reduction in overall mortality were not.

(Those reductions are relative risks, which are on very small baseline numbers.)

Then the article goes on for many pages about how American gastroenterologists do not agree...which isn't terribly shocking, considering the source of the argument. But a number of rebuttals are made, some of which are reasonable (i.e. colonoscopies are one of the few screening tests to actually do something to prevent disease, in the form of clipping polyps), and others of which are quite simply lies ("other studies have estimated larger benefits for colonoscopies" -- yeah, but those studies were bad, and this one was good, which is why we're talking about it!)

Note that American gastroenterologists do a lot of colonoscopies, mostly without good evidence. This was the first major RCT in decades to consider the question at all. The other screening methods have even worse evidence, and certainly no good evidence at the young ages we do them in the USA (currently 40 in men; the studies are all in much older age groups).

Overall, the NORDICC trial paints an incredibly ambiguous picture for the effectiveness of colonoscopy at preventing severe illness or death -- at the very least, the benefits are likely dramatically overstated. Discussing all of this, then turning around and claiming "it works" is an insult to evidence-based medicine.

(FWIW, I'm personally torn on the meaning of the study. I just think that "one thing is clear" line is a particularly odious bit of "journalism" -- not the least because it confuses symptom-free screening with doing something in reaction to symptoms. The rest of the article is pretty fair, IMO, but that line is substituting the opinion of the author for an actual summary of the data.)

Thanks for taking the time to distill the article a bit (more).

I really wish the trial included stool testing. I suspect it would perform very favorably to the colonoscopy, which seems to have very modest benefits to begin with. And the stool test is infinitely easier (and cheaper on a healthcare system).

>The sensitivity of detection of carcinoma is a remarkably acceptable comparison. The multi-targeted stool DNA test is 92% sensitive for finding cancers, which is almost equal to colonoscopy, reportedly at 95%.

https://www.facs.org/for-medical-professionals/news-publicat...

The stool test isn’t as good at detecting polyps but the Nordic study would have shed some light on how much that reduces cancer mortality anyway. This study suggests stool testing compares very favorably to colonoscopy.

https://medicine.iu.edu/news/2019/02/new-study-shows-annual-...

Me too. It would be good to see an RCT between the approaches for asymptomatic people who seek screening.

If i recall, it is important to note that the main analysis in the NORDICC trial was on patients invited to receive screening. As an intent to treat study, not all received screening. There was a subgroup analysis on those that actually received screening, which showed a decent improvement in hazard ratio. The question I had (and will look for when I’m off mobile) is was there a demographic bias in those invited who chose to screen? (Eg higher risk driving their decision). Either way I can control decisions that are not tractable from a public health study point of view. The down side is limited to me— the prep was gross, but my procedure was a breeze. And if something had been found, they can act at that moment. Screening was a no brainer for me.

Yes, this is the main, common counterargument that the OP addresses. This does a pretty good job of showing why that argument is overstated (if not entirely in bad faith), so I direct you back to it.

> There was a subgroup analysis on those that actually received screening, which showed a decent improvement in hazard ratio.

I can't emphasize this enough: read the article. Per-protocol analysis (what you're describing) is incredibly biased. OP shows that it's an overestimate of true effect, and I'd go so far to say that it's completely useless (in general; not just for this paper).

People who argue that NORDICC was wrong because per-protocol showed a bigger effect size should be ignored with prejudice. They don't know how to read or interpret scientific studies, and have a poor understanding of statistics.

> One thing is clear: Screening works. If you’re of the appropriate age, please get screened. If your tubes are acting funny, please get screened without delay.

Screening is for people without symptoms.

If you have symptoms it's not screening, it's diagnostic testing. Diagnosis is important - if you bleed from anywhere you need it to be explained - but there are big differences in how you look at a test that's done for screening vs diagnosis.

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