[doctoring]

This isn’t quite right — I think you’re thinking about circulating tumor cells (CTCs).

These tests on the other hand detect circulating tumor DNA (ctDNA), among other things. It is well known that tumors shed DNA and other material more than normal cells, even at early cancer stage. (Of course, later stage and more aggressive tumors are more indeed likely to shed more.) The detection limit for some of these tests is in the range of single digit copies of DNA fragment per mL of plasma.

Furthermore, the goal isn’t necessarily to detect every cancer as small as it could possibly be. Even if you don’t do a great job at finding all cancers at stage I, you may still save lives by detecting cancers at an earlier stage than they otherwise would have been found. Finding something at stage II instead of III or stage III instead of IV may well mean the difference of a shot for curative resection / radiation. (Whether these tests would be remotely cost-effective at attempting this at population scale... I leave as an exercise to the reader & healthcare system.)

Grail had a paper with some scant info on their test performance in multiple cancer types across all cancer stages. https://www.annalsofoncology.org/article/S0923-7534(21)02046...

[killjoywashere]

> I think you’re thinking about circulating tumor cells

No, I'm very clear on ctDNA, cell-free DNA, whatever you want to call it.

My point stands: early detection goes back to in situ lesions.

The first problem is finding in situ lesions, which is hard.

The second problem is the amount of fear-induced care this generates. These tests are screening tests, so the vendors will lower their operating points to get their false-negative rates down, which will drive up fear, which will drive up follow-on testing, which will drive up follow-on treatment. How much is what matters.

US healthcare costs are already astronomical to the point of becoming a national security problem. And you want to spend more?

[doctoring]

Your original comment stated:

> They won't work for in situ tumors, almost by definition.

Which isn't true. The studies from multiple companies' tests demonstrate that they _can_ detect in situ tumors. Not always super duper well, and not always for every single cancer type, but still.

Whether this is a good idea / cost-effective is another question, and certainly a big deal as you point out.

[Hellbanevil]

My father had a liver tumor for 15 years. We all knew something was wrong, but he said his doctor said it was scar tissue from a hernia operation.

At first diagnosis, the doctors told him to go home.

He later got a call from a doctor who said he would operate. He then called back and said he couldn't. I imagine the hospital looked at the tests, and found it traveled to far, and disallowed the Wonderboy doctor to waste money.

The Wonderboy doctor called back and said sorry. I would have been nice if the doc didn't drag him into office visits, and give him sanctimonious speechs on alcoholism though. This was a good hospital in the Bay Area.

My point is if this study pans out, he probally would still be around?

(If you have money. Get a full body scan. And no they don't pick up on small tumors, but are better than nothing.)

[sizzle]

Sorry for your loss, what were the symptoms that led him to feel that something was wrong?