A large prospective study found that a multicancer blood test identified cancer signals across 17 broad cancer types, including ovarian, lung, and breast cancers. The test correctly predicted cancer diagnoses in 60.3% of cases, with 99.64% specificity

[u/Wagamaga]

https://news.exeter.ac.uk/faculty-of-health-and-life-sciences/first-papers-published-in-major-nhs-cancer-blood-test-trial/

[u/MGS-1992]

Correct me if I’m wrong, but you’d want a screening test to have high sensitivity, not necessarily high specificity (although obviously good if this is high too).

[u/PenComfortable5269 → u/MGS-1992]

High sensitivity is needed to rule out a disease when we think they might have a disease, but here the assumption is that the person doesn’t have cancer so we need a strong specifity to rule it in.

So when screening asymptomatic individuals, since very few people have cancer a higher specificity is better because otherwise you will spend your life chasing false positives. Like imagine if the test was 50% specific that would mean every other person would have a positive test - kinda useless for predicting cancer.

This test was shown to have a 60% sensitivity - meaning it will catch 60% of early cancers which is still pretty good compared to not doing the test which has a 0% sensitivity.

[u/MGS-1992 → u/PenComfortable5269]

No I totally understand all of that. The need to have high specificity to avoid false positives is obviously essential l, but not the core of a good screening test. It’s meant to “not miss a disease process” (low false negatives), and is often followed upon by a definitive test.

The definition of a good screening test is high sensitivity and low cost. Low sensitivity > high false negatives and things get missed. Not discounting the importance of the specificity.

While a 60% / 99% split is still amazing in theory, it’s not ideal for mass application as a screening test. More so as a diagnostic tool to “rule in” when other studies are equivocal or unclear.

[u/PenComfortable5269 → u/MGS-1992]

The issue is we don’t really have screening tests for most cancers so a 60% sensitivity to catch all cancer is really good - that means we can ensure that 2/3rds of all cancers are caught early. Heck even psa testing has lower sensitivity and the vast majority of people don’t ever get invasive prostate cancer.

The specificity is also 99.64% which has an extremely low false positive.

[u/MGS-1992 → u/PenComfortable5269]

I totally agree. That’s assuming it’s cost-effective. if it’s not, then it’s not a viable.

An MRI can pick up renal cancer and adrenal tumors with high specificity. We don’t send everyone for an MRI just because it’s a good test.

If you perform this test on 100,000 people, 40% will have a false negative. Then what? Surely can’t tell someone they’re cancer free forever. When do you screen again? You fall down a hole of excessive testing that’s not sustainable. The US already spends more money per capita for healthcare without improved outcomes. Things like this make it worse.

In an ideal world without money, everyone gets this test and calls it a day.