There are some ideas about making it triggerable. So first you load the cells with a protein that is ready to start shredding but is inactive. Then you trigger it with a second compound.
That's how we deal with HIV. No single HIV therapy (so far) is effective enough to suppress the virus all by itself, but a combination of them provides a barrier that is too high for mutations to jump.
The new therapies will also likely be applied after surgical resection and/or classic therapies to reduce the bulk of the cancer.