Comment by lich_king | Hacker News Reader

Comment by lich_king | Hacker News Reader

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No. To argue for the benefit of the procedure, you need to show a difference in outcomes. Not that it can detect something, even if it could (which whole-body MRIs clearly don't). That the detection improves your chances of survival.

If you have an growing mass in your body, then if it's cancer, after a year, it might be too late for treatment. Or it may turn out to be nothing: a benign tumor / cyst / fat deposit in an unusual place. Or it may be slow-growing prostate cancer that you can live with for another 20 years, and maybe it's the chemotherapy that will do you in. It's really not that clear-cut in medicine.

To give you have another example: let's say that the risk of appendicitis in people who have an appendix is 1%. And the risk in people who had an appendix removed is 0%. Does this justify proactively removing the appendix? No, because the consequences of complications are much higher than the harm you're preventing. The same applies here: detection, even if 100% accurate, doesn't mean anything. You need to show that what you do with the result actually helps.

The difference in out come is

With my change: 95% of people who are shown scans have cancer and are treated earlier. 5% of people do not have cancer and get CT scans. 0.5% of people get useless biopsies Without my change: many of those 95% die, the 0.5% do not get useless biopsies

And the beauty of this is you can pick the percentage!

> If you have an growing mass in your body, then after a year, it may very well no longer make a difference whether you treat it or not. Or it may be that you would have lived another 20 years just fine

This is just wrong for many parts of the body. In your brain? Your lungs? Growing for a year between 3 scans 6 months apart? Extremely unlikely to be benign

> The same applies here: detection, even if 100% accurate, doesn't mean anything. You need to show that what you do with the result actually helps.

This is wrong. If you had a 100% accurate cancer detector, fewer people would die of cancer with no downside

> With my change: 95% of people who are shown scans have cancer and are treated earlier. Without my change: many of those 95% die

Why? What happens if the cancer still doesn't respond to treatment even when detected early? Or, to the contrary, if the cancer also responds to treatment when it starts becoming symptomatic?

That's why we have studies to understand if screening is a good practice or not. It's not that clear cut.

> With my change: 95% of people who are shown scans have cancer and are treated earlier. 5% of people do not have cancer and get CT scans. 0.5% of people get useless biopsies Without my change: many of those 95% die, the 0.5% do not get useless biopsies

You assume that treating cancer automatically improves the outcome. Treating cancer often kills you, so treating a non-fatal tumor can easily be a bad decision. And a lot of the tumors found by agressive scans are like that, but we don't know yet how much exactly and how to tell one from the other. It's a new question that requires decades-long observations to answer.

> This is wrong. If you had a 100% accurate cancer detector, fewer people would die of cancer with no downside

You're saying it as if detection somehow cures cancer, it doesn't.

> You're saying it as if detection somehow cures cancer, it doesn't.

No, I didn't say the detector would cause cancer to be cured. I said fewer people would die with no downsides. If treatment is sometimes harmful then the detector also fixes that, you'd never treat people without cancer

No, the detector doesn't fix that, that problem is not treating people without cancer. The problem is treating people with cancer that won't kill or harm them during their lifetime. In this case even a low risk treatment becomes harmful, let alone cancer treatments.

Your claim is equivalent to claiming that most cancer treatment is net harmful btw

and this is obviously false, especially for cancers detected earlier

Whether treatment is net harmful or not depends on the level of the risk with no treatment. If you apply treatment with 15% chance of severe side effects to a tumor that will kill the patient with 50% chance in the next five years, of course it's net positive. If you apply it to a first-stage cancer that has 10% chance of progressing to the second stage, the very same treatment will be net harmful.

So no, most cancer treatments aren't net harmful now, but they likely will be in a world where your programme is implemented. Even something as "simple" as biopsy has mortality rates far from zero. Applying it at scale may not have the effect you expect. And surgeries and chemo are much worse.

But do you see how crazy that sounds? If we know the numbers, we would just not do the treatment in those cases.

And in reality it's not actually close like this. Early treatment is so overwhelmingly better than it completely dwarfs all considerations of biopsy risk.

Late stage lung cancer has less than half the 5 survival of early stage, and around 50% of lung cancer detection is late stage. That's around 30000 lives you could save every year from just lung cancer.

Let's say you don't protocol for all adults. Typically post CT or PET at most 10% get a biopsy. So let's say we increase the false positives that lead to CT or PET by X% of adults. That's 270M * X additional biopsies. Lung biopsy mortality is under 2%.

So the worst case you need a false positive rate under 5% for this to he net beneficial for lung cancer. That's low but with 3 scans 6 months apart and a good radiologist, it's not unreasonable

I believe I've assumed the worst case for all the quantities. In reality the addition screened people would have much lower CT detection rate than the background population, and biopsy mortality has been decreasing. Plus you can do this for only people above 40 where the benefits are higher

Yes, IF we know the numbers, that's the whole problem. Unprompted full-body MRI scans turn up a completely new probability distribution. We CAN'T know the numbers as of today, it takes decades of controlled studies to get them. (Which is exactly what doctors advocate for)

Even for something as studied as colon cancer it's still controversial whether mass colonoscopies are better than occult blood tests. US sticks to the former, Europe to latter. US have higher rates of polyp removal, higher rates of cancer detection, higher rates of surgeries and ... higher mortality rates than EU. Why this happens is being studied today, there are some early results. What is absolutely clear though is that higher detection rates don't automatically lead to better outcomes, it can easily be the opposite.

Or take something as simple as sunscreen. It's well-known that sun exposure for light-skinned people can cause cancer and sunscreen is advised. A few multi-decade studies have shown that while it indeed eradicates the skin cancer it also shortens the life expectancy by a few years.

Primum non nocere, doctors and scientists are unsure whether sunscreen should be applied at scale and you effectively call for mass biopsies and surgeries.

So if this is true, it seems that we must accept that many people will die of cancer we could have detected and cured with frequent scans, because doing frequent scans will overall cause more harm to people who didn't need treatment. So the overall death/harm rate would be worst with more frequent scans?

Isn't that then just a problem with the scan and diagnosis? With more frequent scans it seems highly unlikely that we wouldn't improve this process and end up in a better place.

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