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Blood test that finds 50 types of cancer is accurate enough to be rolled out

theguardian.com

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Re: Blood test that finds 50 types of cancer is accurate enough to be rolled out

#281

Post by jghn »

graeme wrote: post #251
plank_time wrote: post #137

Earlier quoted context omitted.

It’s pretty easy. If blood test says “liver cancer positive. Colon cancer negative.” you check the liver for cancer. No need to check the colon for cancer. No need to scan the entire body for lumps.

Not that easy. “Check the liver for cancer” has lots of risks: surgery and the resulting tissue injury. I’m generally inclined towards the position of more testing....but there are very real tradeoffs to any of the interventions that a blood test could prompt.

Also, you might have identified liver cancer that came from the patient's kidney. Or a colorectal cancer that came from the patient's liver.

Re: Blood test that finds 50 types of cancer is accurate enough to be rolled out

#282

Post by epmaybe »

I don’t have much to add to the discussion here. Sensitivity is poor, specificity is pretty good and could be better if used as a confirmatory test(?). What I found interesting in the comments is how many people involved in healthcare lurk on a forum very much not dedicated to healthcare. Kind of cool. You all should chime in more, I learned a lot.

Re: Blood test that finds 50 types of cancer is accurate enough to be rolled out

#283

Post by jacquesm »

ggrrhh_ta wrote: post #250
jacquesm wrote: post #204

Earlier quoted context omitted.

Yes, they can, but not in a blanket fashion where a test with a relatively high false positive rate and a relatively low sensitivity (between 18 and 50% for this particular test) is released without patient outcomes as the main driver of whether or not to apply the test absent further symptoms. Whether this test is one that can serve in that particular role is definitely not something that has already been determined…

Well. With a bad test, what is necessary is to improve the test. The argument "outcomes are worse off with more absent symptoms testing" is really saying that symptoms is more predictive than the test itself: test is positive if [symptoms & positive result] test is positive or neutral if [no symptoms & should have been screened & positive result] and test is negative if [no symptoms & should not have been screened &…

You are visibly making progress in your understanding of the problem, for which you are to be commended, especially if you are a complete layperson in this field. Thank you.

This test isn't a 'bad test', though applying it in the wrong way can lead to bad outcomes. This is why tests used absent symptoms have to have a false positive rate that is much lower than the base rate at which the disease occurs. These tests - unlike software tests - should not be thought about in absolute terms but in terms of probability, so a positive test indicates a probability that you have a specific disease, but it is very well possible that you do not have it, and a negative test indicates a probability that you do not have it - but it is very well possible that you in fact do have the disease. And the reasons for a false positive or false negative may have nothing to do with the test itself, but could easily be an environmental factor or some benign aspect of the test subject that was not accounted for when designing the test.

Whether or not a test is suitable for mass screening hinges on the factors above, the base rate for the disease, the age of the group being tested, in some cases gender and so on. In order to have a positive outcome across the population all these factors have to be taken into account and by the time that you have done so there are - unfortunately - at the moment no miracles to be had. But combinations of knowledge, for instance a genetic pre-disposition to a certain disease + a positive test can have much higher signal to noise ratios than either by themselves.

But make no mistake: this is an important development in medical diagnostics and it may very well be that once more evidence has been collected and some of the kinks have been worked out that this particular test or an improved version of it can be applied in a screening setting for one or more of the cancers that we currently have no reliable detection method for and that could be cured if detected early enough given a high enough base rate and a low enough false positive rate.

Note that the scientists behind the project are very careful with their statements and that the reporting on this was actually quite neutral and trends to cautious optimism, which I think is warranted, but until the result of the new studies is known it is way too early to shout 'revolution'.

Re: Blood test that finds 50 types of cancer is accurate enough to be rolled out

#284

Post by theptip »

dangerlibrary wrote: post #170
axxto wrote: post #154

Earlier quoted context omitted.

The point of this is not that you get a definitive diagnosis; it's just a somewhat reliable marker on whether you may need to be concerned and get more accurate (but more harmful) imaging or invasive tests to rule out something.

You only need one false positive test result that ends up with a colonoscopy to understand how costly and uncomfortable these errors can be. (I'm using an uncomfortable and illustrative example, but a colonoscopy is honestly pretty safe and boring as invasive clinical diagnostic procedures go)

Perhaps a better example than you intended -- recently colonoscopies are being considered more risky as a regular screening tool, because the procedure itself can result in harms, including (rarely) death. Not an expert here, but it seems they are still used in a fairly wide age group, but the recent trend is to be more cautious about their usage, as particularly for older patients they are more risky vs. the potential benefits. [1]

However I think this concern would be reduced if we had better first-line screening like the tests in TFA; the harms come from using a relatively-risky assay like colonoscopy for regular screening in healthy individuals, whereas if we had better noninvasive screening, the colonoscopy could be reserved for patients where there's a higher probability of a positive diagnosis.

[1]: https://jamanetwork.com/journals/jama/fullarticle/2529486

Re: Blood test that finds 50 types of cancer is accurate enough to be rolled out

#285

Post by fierro »

TaupeRanger wrote: post #96
reacharavindh wrote: post #3

This is one of those medical revolutions that I am waiting dearly for. Facilities that are not hospitals(to avoid the risk of occupying medical devices that sick people need) built to _regulary_ check up otherwise healthy people for preventive care. Heck, I have so many alerts defined on my monitoring setup for servers to watch for signals of failure before they get too big. But, my own body is not observed until som…

Actually you don't want this, and you are describing a nightmare scenario that everyone who studies health policy understands all too well. Mass screening of healthy people will result in extreme iatrogenics and unnecessary psychological damage and stress (which leads to physical effects as well), not to mention overwhelming the medical system. The fact is that many things that could be detected will never result in…

this is a paternalistic point of view. People should be entitled to accumulate data about their own body -- any "negative" ramifications of this are personal problems.

Re: Blood test that finds 50 types of cancer is accurate enough to be rolled out

#286

Post by fierro »

TaupeRanger wrote: post #133
throwawaynotmd wrote: post #109

Earlier quoted context omitted.

The argument you’re making has always bothered me because it’s hiding the ball. If finding something that otherwise carries no symptoms is best left untreated, then the fact that you found it should make no difference to the decision. The doctor should say that the best course of action is to do nothing. More information can never be harmful. If you know information is best not acted on in the abstract, then you also…

Lots of problematic assumptions in your reply. >If finding something that otherwise carries no symptoms is best left untreated, then the fact that you found it should make no difference to the decision. The doctor should say that the best course of action is to do nothing. More information can never be harmful. Absolutely and demonstratively false. There is an entire field of health policy that destroys this harmful…

you're conflating "pushing for further tests" with "pushing for further treatment.' IMO, everyone should be entitled to as much data accumulation as they want. Insurance companies can set reasonable thresholds, but if I want to pay out of pocket to get bloodwork done, that should be easy to get.

Whether or not a doctor prescribes/advises a certain treatment is still firmly in their domain. The amount of biomarkers/biological evidence a patient has shouldn't sway a doctor's decision to alter a treatment plan. As a reasonably smart non-medical professional, I would rather have more data than less data, and it's paternalistic and a little condescending to say "no, you shouldn't actually take diagnostic tests because 'having that information might freak you out'"

Re: Blood test that finds 50 types of cancer is accurate enough to be rolled out

#287

Post by TaupeRanger »

skybrian wrote: post #280
TaupeRanger wrote: post #133

Earlier quoted context omitted.

Lots of problematic assumptions in your reply. >If finding something that otherwise carries no symptoms is best left untreated, then the fact that you found it should make no difference to the decision. The doctor should say that the best course of action is to do nothing. More information can never be harmful. Absolutely and demonstratively false. There is an entire field of health policy that destroys this harmful…

I have no expertise here but I worry that these trials are studying the decision-making processes around how people decide to use the information from these tests, rather than the tests themselves. How people use information varies, so the data might not have external validity - it’s culture specific, and cultures differ. Cultures can also change through accumulated experience. So do the people studying these things…

That is a very important point. This is why multiple studies are needed that across time, location, culture, etc. The more data a doctor has the better decisions they can make for their specific patients.

Re: Blood test that finds 50 types of cancer is accurate enough to be rolled out

#288

Post by UnFleshedOne »

rackjack wrote: post #249
JumpCrisscross wrote: post #225

Earlier quoted context omitted.

> these cures are often brutal Heart disease is a huge deal. It ruins your life. (Maybe not in all caps.) Nevertheless, we regularly test for it, including with techniques with high rates of false positives. Few panic because almost everyone knows someone who got a false positive and didn't promptly keel over and die. If healthy adults are screened for cancer, there will be cultural memory of people who got a false p…

I don't enough about heart disease treatment to comment on the degree it ruins your life. People already get further testing. People already get second opinions. In the time you are changing your lifestyle (a good option for helping treatment, I agree) and increasing monitoring you could already be progressing beyond treatability. You can argue about whether it's alright to tell sub-1.5 million people each year who d…

> In the time you are changing your lifestyle (a good option for helping treatment, I agree) and increasing monitoring you could already be progressing beyond treatability.

That's actually a very good argument for early testing.

And needlessly scaring a some people into eating better and exercising more is about as bad as not screening them at all to avoid needless anxiety.

Re: Blood test that finds 50 types of cancer is accurate enough to be rolled out

#289

Post by throwawaynotmd »

TaupeRanger wrote: post #267
throwawaynotmd wrote: post #258

Earlier quoted context omitted.

I should say, if you know ex ante that certain results are not worth acting on, then when you actually get those results ex post, you should ignore them just the same. So actually running a test cannot formally be the problem.

That is not how medicine works, especially with cancer. Very often we simply don't know whether or not to "ignore" something. But the harms of knowing are not zero, and therefore screening can itself be a net negative. That's why a well powered RCT is required to say whether it benefits patients or not.

We have a more detailed exchange going on elsewhere in this thread, with my latest comment, addressing your more detailed points, here: https://news.ycombinator.com/item?id=27630947

Re: Blood test that finds 50 types of cancer is accurate enough to be rolled out

#290

Post by nmz »

rackjack wrote: post #184
plank_time wrote: post #147

Earlier quoted context omitted.

We don’t give colonoscopies to 20 years olds because it’s an expensive, invasive test with a low rate of cancer. We don’t give mammograms to under 40 year olds these days because the same and it’s notoriously inaccurate. We give blood glucose level tests and cholesterol tests to everyone every year at the physical because they are cheap and easy to administer. Even though the effects of both may take decades to have…

> It correctly identified when cancer was present in 51.5% of cases, across all stages of the disease, and wrongly detected cancer in only 0.5% of cases. If all 300 million Americans get blood tested each year, that is 1 and a half MILLION people who are falsely told they have CANCER. One and a half MILLION people whose life gets turned upside down, WRONGLY, due to a blood test -- at least, until they take a second o…

Maybe I'm misunderstanding this but a 0.5% false positive rate and a 51% positive rate means that you still get a 50% TRUE positive rate instead of the current rate, which is 0%. And then after you can follow up with a test that is more accurate. Everything has an error rate, even pregnancy tests do, and nobody argues that we should not use pregnancy tests.
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