I’m probably making some false assumptions here, but bear with me for a moment…

Malignant cells invade adjacent tissue.

Tissue may be normal or cancerous. Hopefully cancer cells can’t tell the difference.

Treatment is a natural selection process. Cells that survive the treatment proliferate and form treatment-resistant recurrences.

My idea is this: Examine a tumor for an area that is sensitive to chemotherapy or another treatment. Remove these cells (along with the rest of the tumor in a patient, but don’t use the rest), optionally genetically engineering them to curtail their ability to evolve, making them secrete some sort of treatment molecule (a telomerase antagonist would be a very good choice, IMO), or doing other things that may help treat the cancer. Grow these cells.

Now inject them back into the patient at the original tumor site.

Wait a little while and then blast the whole thing with whatever treatment those cells were vulnerable to.

The optimal hypothetical scenario is that the vulnerable tumor cells displace the original tumor, invading those cells just as they would invade normal tissue. The treatment then eradicates them, leaving the patient with virtually none of the vulnerable cells and substantially fewer resistant cells than they would otherwise have. Not a complete cure, but it should boost survival time significantly and may even boost cure rates due to elimination of micrometastases.

I’ll keep thinking. I’m still officially researching on the diagnostic side rather than the treatment side, but perhaps I have an audience (or at least someone to tell me why it won’t work) for these sorts of ideas now that I work with oncologists.