Grail's "Galleri MCED" (Multi-cancer Early Detection) panel is a simple blood test you can get drawn for a self-pay of approximately $1000 US. It's not FDA approved for official diagnostic use, but does have their approval as a "Lab Developed Test." You can call Grail, speak with one of their physicians/reps, and likely get the test approved, without waiting for local docs or what your primary oncologist thinks.

They will send you a kit in the mail (US only?) which you can take to a local doctor/lab for the blood draw and return shipping to Grail, with results in about 2 weeks.

Although it completely failed to detect my pancreatic cancer recurrence before other methods (rising CA19-9 and MRI), I am only a sample of one, and they claim some reasonably good statistics for pinpointing the likely origin of cancer cells as well as their presence. Scroll down this link to the section about "88% Cancer Signal Origin Accuracy" at https://www.galleri.com/hcp/galleri-test-performance

There's a little more discussion in this Mayo Connect thread:
https://connect.mayoclinic.org/discussion/galleri-test/
Despite its imperfections, if I even suspected a possible cancer, I would consider this test. If I had evidence of cancer with unknown origin, and doctors in "wait-and-see" mode or having other difficulties identifying the origin, I would be first in line to get the test done and hopefully help them along.

With the caveats above, if anyone has a chance to use this test, please post replies in the forums here!

Thanks and best wishes.