[DennisP]

No, I mean you take the test and if it's positive then present options like this:

Risk of death: X% with treatment, Y% without treatment.

Risk of side effect A: X% with treatment, Y% without treatment.

Those numbers take into account the rate of false positives and false negatives. They are clear and understandable.

There are definitely situations in which you shouldn't test: where the rate of the cancer is low, the false positive rate is high, and the risk of treatment is high. In that case, the numbers can show that risk of death is higher with treatment than without, so while (noninvasive) testing doesn't make things worse if we're giving clear numbers, it doesn't help either; we might as well not test at all. But that's not true for everything. As for side effects, we should give patients clear numbers like this so they can make informed decisions.

Adding up the number of false positives and negatives, and the number of patients with various outcomes, is not comparable to using AI.

[vc8f6vVV]

You are also presented with a choice: you take a test and you die in X% because of the test itself (there are no non-invasive tests, even IV is potentially dangerous), or you may be diagnosed with cancer with Y% chance of right diagnosis and Z% of lethality. Math is getting much more complicated. Now consider that only 2.5% women will die from breast cancer, but 97.5% others will get X-ray exposure once a year (with 100% test coverage of course). X-rays are know to cause mutations and thus cancer. Add to this money spent on tests that can be used to find a cure (we don't have unlimited resources).

[throwaway290]

Simply having the information that they maybe have cancer, people are not great at just living unstressed because it may or may not be a false positive. And stress is known to cause a lot of problems including weakening immune system.

[DennisP]

Which is why you only test in situations where, if the test is positive, you have better odds if you treat.

[throwaway290]

Better odds to live longer or have good life? Looks like this study says it's definitely not the former?

[DennisP]

Untreated cancer is not without its effects on quality of life.

As I said above, with a positive test, work out the numbers for death and other unpleasant outcomes, with or without treatment, and let the patient decide. If those numbers would say not to treat regardless of test results, then don't test.

The study just says that most, not all, cancer screenings don't extend life. And it doesn't say whether doctors are giving patients the numbers I described. I suspect they aren't, which likely means that sometimes they treat even when these numbers would say they shouldn't.

[throwaway290]

Sure, but cancer != positive test because of false positives. Therefore the question of odds.

I like your idea of working these things out statistically but by your phrasing it's not necessarily what's being done (as in there are no reliable enough numbers for odds that matter).

But even if those odds were available, no matter what patient chooses, once you tell then there is a positive result, the fact that false positive is possible and odds are not in favor of treatment so they make a choice to do nothing does not mean they get to live a normal life from now on. Patients are not pure bayesian choice machines. The choice you make will affect you in big unknown ways and the existence of such choice already affects you until your EOL and has repercussions. That cancer was detected in your body cannot be "unheard" or "unread" back. Maybe you manage to deal with it, maybe you will live in constant stress. and of course chronic stress is connected to tissue inflammation, sleep disruption and other issues.

Therefore your argument that screening is automatically good does not seem to be convincing to me

[DennisP]

Right the numbers for "positive test" should include false positives. That's part of my point. I've worked out a sample calculation if you want to see it. We could get fancy with error bars but I don't think that's necessary for any common cancer, and rare cancers shouldn't be tested for anyway since you'll mostly have false positives.

As I said above, I don't think that screening is automatically good because in some cases, working out the above numbers will tell you not to treat even if you had a positive test. Those cases should not be tested since they're not actionable anyway. That would likely be the case for a rare cancer.

I agree that a false positive is not great. But if you have the data, then the impact of false positive tests is already included in your data. You're comparing the total rates of death and other unpleasant outcomes for a tested population vs. an untested population.