[tansey]

The problem with the idea of cheap screening tools is Bayes' theorem. If doctors go ordering this for most people since it's just a blood test, and if only 1% of people ever really have cancer when tested then the 1% false positive rate means there's only a 50/50 chance you have cancer given the test is positive.

[rplnt]

So that's one "wasted" advanced screening for one where cancer is found. That seems great to me.

Also, I assume it would be mostly done on higher risk patients (certain work conditions, certain age, etc..). Only once in couple of years on younger population for example. Or if it's really cheap everyone could get it and then there could be more focused blood screening done next so you don't have to get full body cat scans.

[vidarh]

It's not that simple. If the worst effect was some unnecessary secondary screening, it would be a no-brainer.

But first of all you need to account for the negative effects of a false positive, and they are much worse than that. They include anything from stress and psychological effects, cost and risks of all the additional screening, to the much worse issue that you also need to account for the fact that for some cancers in some instances it will be hard enough to determine if the growth is malignant in the sense that some proportion of cancerous growth will never pose a threat to the patient, but once diagnosed there tends to be a strong pressure to treat. As a result too frequent screening will save some, but will also result in a large amount of unnecessary chemo, radiation therapy and/or surgeries - all of which come with risks in addition to the pain and discomfort.

Then you need to account for frequency of testing. A 1% false positive rate per test looks distinctly worse if the test is repeated every year for a 10-20 year timespan, for example.

Then you'll also want to account for how much it improves outcomes. If the cancers it detects are ones that would generally be detected in time anyway, and/or have low mortality, and where treatment outcomes are good, the incremental improvement would not necessarily be big enough to justify the negatives.

For breast cancer, for example, there has in recent years been a push to reduce large scale routine mammogram screening because it's not clear if it does more good than harm for many groups of patients (in large part because it leads to overtreatment). This article goes into some of the issues related to that in some detail (and presents both proponents and detractors of large scale screening):

http://www.healthbeatblog.com/2009/04/mammography-screening-...

[the_af]

Wasn't there a similar argument (linked to here on HN a few years ago) against early screenings for prostate cancer using highly sensitive techniques?

If I remember correctly, the argument went like this: early screening may detect some forms of prostate cancer which, given the estimated natural lifespan of the patient, would have failed to kill/discomfort him before he died of other causes. But once it's been detected, the recommendation will be to treat the cancer; and treatment has a chance to cause discomfort (such as impotence) right now. So in effect, early detection of some forms of prostate cancer may negatively impact the quality of life of patients who would have otherwise lived a normal life without noticing the cancer.

I might be remembering some details incorrectly.

[cratermoon]

https://academic.oup.com/jnci/article/101/19/1325/1073822

"Given the considerable time that has passed since PSA screening began, most of this excess incidence must represent overdiagnosis."

[rplnt]

I'm not sure the pressure to treat is a real issue. Some types of cancers (lymphoma for example) are only monitored in early stages. So if this would result in increased early detection, it might be a standard procedure to just keep an eye on the cancer, even for wider ranges. It's better than waiting for symptoms to appear (and the tendency for people to ignore the symptoms for a year before seeing a doctor).

[vidarh]

See the link - it includes details about studies done on breast cancer for example where overtreatment is a real issue. This is not a hypothetical concern, but a concern that's significant enough that large scale screening programs have scaled back in some countries in response.

[tptacek]

It was a real issue for relatives of mine, who had to argue down doctors ordering invasive procedures for things that over the long term turned out to be non-issues.

[taneq]

But it means if you test negative you can just stop worrying about it completely.

[cfmcdonald]

No it doesn't, since of the people known to have cancer who were tested, only 70% tested positive.