Something tied to what you said that is often not appreciated by people is that early detection can actually cause harm. In the example you gave of slow growing prostate cancers, in many cases people will now undergo treatment due to the early detection and the treatment winds up being far worse than the cancer itself would ever have been.

As the technology improves it's getting better at making predictions on the severity of the cancer and that can be used to guide treatment, or lack thereof. It's still far from perfect however.

> early detection can actually cause harm. In the example you gave of slow growing prostate cancers, in many cases people will now undergo treatment due to the early detection and the treatment winds up being far worse than the cancer itself would ever have been.

I have never quite bought this argument. ISTM it's not the early detection that causes harm -- it's the inappropriate treatment of early detected cancer that causes harm.

Yes, that's exactly what it is. Thus the argument is that indirectly early detection causes harm. As I mentioned later on in my post a lot of current research is going into determining if and when treatment must be done instead of the more common behavior of just diving in wholeheartedly.

"Early detecting causes harm" sounds absurd. That's akin to saying that "eating food" (and not dying from hunger) leads to harm from cancer treatment.

We also have a case study of over diagnosis from Korea:

http://www.npr.org/sections/health-shots/2017/05/09/52756929...

"South Korea is the poster child for the problem of overdiagnosis" of thyroid cancer, Welch says. About 15 years ago, doctors there started a mass campaign to screen for thyroid cancer. That vastly increased the rate of thyroid cancer, to the point that it exceeded cases of breast cancer and other common malignancies.

Yet Welch notes that the mortality rate from this cancer didn't change at all. "So all these extra cases were cases of thyroid cancer that weren't destined to bother people," he said. Instead, that rash of overdiagnosis sent people into needless surgery.

Harmless thyroid tumors are surprisingly common. Decades ago, pathologists in Finland noticed that more than a third of the people they saw in autopsy had thyroid tumors, but the cancers had no negative consequences.

No, it's not absurd at all.

Cancer treatment is not benign and (believe it or not) not all cancers will always causes harm.

https://sciencebasedmedicine.org/the-uncertainty-surrounding...

For instance, in 2012 a study in the New England Journal of Medicine (NEJM) by Archie Bleyer and H. Gilbert Welch found that, while there had been a doubling in the number of cases of early stage breast cancer in the 30 years since mass mammographic screening programs had been instituted, this increase wasn’t associated with a comparable decrease in diagnoses of late stage cancers, as one would expect if early detection was taking early stage cancers out of the “cancer pool” by preventing their progression. That’s not to say that Bleyer and Welch didn’t find that late stage cancer diagnoses decreased, only that they didn’t decrease nearly as much as the diagnosis of early stage cancers increased, and they estimated the rate of overdiagnosis to be 31%. These results are in marked contrast to the promotion of mammography sometimes used by advocacy groups. Last year, the 25 year followup for the Canadian National Breast Screening Study (CNBSS) was published. The CNBSS is a large, randomized clinical trial started in the 1980s to examine the effect of mammographic screening on mortality. The conclusion thus far? That screening with mammography is not associated with a decrease in mortality from breast cancer. Naturally, there was pushback by radiology groups, but their arguments were, in general, not convincing. In any case, mammographic screening resulted in decreases in breast cancer mortality in randomized studies, but those studies were done decades ago, and treatments have improved markedly since, leaving open the question of whether it was the mammographic screening or better adjuvant treatments that caused the decrease in mortality from breast cancer that we have observed over the last 20 years.

To echo the other responses with a practical example, suppose you were to have a slow growing prostate cancer. Suppose that there was a 0% chance it'd actually cause you any real harm. This is a not at all uncommon scenario.

Now suppose an early screen detects this cancer. Since we still have difficulty discerning whether or not your cancer is really "bad" or not you'll likely undergo immediate treatment. This treatment leaves you feeling horribly ill for the duration with all sorts of side effects. After treatment you're left with urinary leakage and erectile dysfunction.

I don't know about you but if you were to tell me that I could live the rest of my days with a minor cancer growing in my body minding its own business I'd choose leaving it there vs the side effects of the treatment.

> And the deadliest cancers are the ones that grow quickly, quickly enough that early detection is extremely difficult.

If a blood test can detect it, couldn't it be economically feasible to have people do it monthly, with a mailed kit and return envelope? Doesn't seem like much more work than taking vitamins, certainly less than going to the gym.

How do you think your blood test can tell the difference between slow-growing and fast-growing prostate cancers? Most men die with small prostate tumors.

I'm sure there would be types of cancer that would benefit, but it would involve a lot of study of outcomes.

> How do you think your blood test can tell the difference between slow-growing and fast-growing prostate cancers?

Would it need to? If your test ever came back postive, you'd go into the doctor, presumably retest to confirm, and then start appropriate treatment, regardless of how fast-growing the discovered cancer was.

To be clear: I'm not arguing, just genuinely curious as this isn't a subject I know much about.

The appropriate treatment depends on the risk of death. Chemotherapy is among the worst - probably 20% of people who get chemo die because of the chemo. If there's a 20% chance that the cancer will kill you, there's zero utility to a treatment that has a 20% chance of killing you.

Since none of the treatments we have are 100% effective, they can be worse than useless, actually increasing the overall death rate, and ensuring that the end of life is long, drawn-out, and horribly painful.

Understood. But my original question was inspired by greg's claim that early diagnosis of fast-growing cancers typically won't help, because they're so fast. I was asking if it would feasible to do monthly at home blood tests as a way to detect even rapid growth cancers (and assuming that would be enough time).

The point you're making seems orthogonal to me. Unless you're claiming that treatment is never worthwhile for such cancers, no matter how early they're detected, but Greg's original statement seemed to imply otherwise.

I read Greg's claim (and it's similar to mine) as meaning that there's no test to distinguish between fatal cancers and benign cancers, and this test doesn't claim to be such a test. Even if you have a test that's 100% accurate at detecting cancer, it's only useful if it only detects cancers that are likely to be fatal, otherwise unnecessary treatment will be expensive, both in dollars and in deaths.

>Chemotherapy is among the worst - probably 20% of people who get chemo die because of the chemo.

That's likely not right. I would believe something more boxed in...like 20% of patients who die within 30 days of starting chemotherapy died from it versus the cancer.

That's a recipe for over-treatment, which is already commonly happening for prostate cancer. As I mentioned earlier, it's very important to study outcomes! And not just do what seems reasonable.

Meaning you'd be treating false positives? I assumed the blood tests were coarse-grained, but surely there are more reliable tests that you could do if you tested positive on a blood test. Or are there not?