There will never be a single cure to all cancers. Different cancers have different underlying mechanisms and affect different tissues.

I think this is untrue. All work by uncontrolled replication of cells. This is why nanotechnology had the promise of being able to eliminate cancer - imagine a nano scale robot regularly cycling through your body on occasion, looking for and eliminating cancerous growths.

Drugs, though, probably have very limited potential.

Maybe. The fact that some animals are especially immune to cancers suggest there are ways to prevent the outcome (cell replication/mutation).