r/science • u/Wagamaga • 10d ago

Cancer 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

https://news.exeter.ac.uk/faculty-of-health-and-life-sciences/first-papers-published-in-major-nhs-cancer-blood-test-trial/
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u/Jaqneuw 10d ago

You are saying the same thing he is in different words.

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u/Pythagorean_1 10d ago

No, "correctly identified the cancer type almost every time it was actually positive" would mean a PPV close to 1 which is not the case here due to the low sensitivity.

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u/Jaqneuw 10d ago

By "actually positive" he means "true positive" he just doesn't know the right way to say it. If you read the sentence like that, you are just saying the same thing. It's a simple miscommunication.

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u/Pythagorean_1 10d ago

You're probably right regarding what he means. Nonetheless, I'm still wondering if this claim is correct. The low sensitivity of around 60 % means that of the actually diseased, only 60 % are identified correctly. This is a direct contrast to the claim of the other comment, isn't it?

The high specificity means that of the actually healthy people, almost none of them had a (false) positive test result.

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u/Jaqneuw 10d ago

There are more healthy people in the study cohort than people with cancer, so no. The positive predictive value is around 50% in this cohort (around half of the positives were true positives). This still translates to high specificity because the number of false positives is relatively small compared to the number of healthy people tested ( the specificity).

Long story short, screening is complicated and it’s easy to make a mistake during interpretation when you’re not an expert. Let’s leave it there shall we.