Cancer DNA is detectable in blood years before diagnosis

The big secret is that they could detect cancer very early in most people, but the health care companies don't want to pay for the screening. You can pay out of pocket for these procedures. I was told this by a cancer researcher

EDIT:

Adding these caveats:

1. There is a ton of nuance in the diagnosis, since most people have a small amount of cancer in their blood at all times

2. The screenings are 5-10k + follow up appointments to actually see if its real cancer

3. All in cost then could be much higher per person

4. These tests arent something that are currently produced to be used at mass scale

The not so big secret is that we can detect cancer early in a lot of people, but we also would detect a lot of not-cancer. We don't currently know the cost/benefit of that tradeoff for all these new types of screening, and therefore insurers and health systems are reluctant to pay the cost of the both screening and the subsequent workup. This is not just a financial consideration, though the financial part is a big part -- the workup for those that end up as not-cancer has non-negligible risks for the patients as well (I have had patients of mine suffer severe injury and even die from otherwise routine biopsies), and on top of that, some actual cancers may not really benefit from early discovery in the first place.

This is not to downplay the potential benefit of early cancer detection... which is huge. And in the US/UK anyway, there are ongoing large trials to try to figure some of this stuff out in the space of blood-based cancer screening, as part of the path to convincing regulatory bodies and eventual reimbursement for certain tests. As mentioned, you can currently at least get the Galleri test out of pocket (<$1k, not cheap, but not exorbitant either), as well as whole body MRIs (a bit more expensive, ~$2-5k).

Or cancers that aren't clinically relevant.

Many prostate cancers, for instance, are slow growing and won't kill you before something else does. If you try to take that kind of cancer out surgically or zap it with radiation or chemo the side effects could be severe.