We're talking about genetic therapies that would make cells less prone to mutating into cancerous cells. This would have no effect on cells that are already cancerous, introduced from an outside source.
I mean, I guess it would depend on how you are introducing the gene. How many cells it is getting into.
But if it causes defective cells to suicide, why would it matter where the defect is coming from? I don't think we really have a good handle on what causes cancer. I suspect more cancer is due to some infectious agent than is generally believed and we know genetic variations have significant impact on the immune system and its ability to function at all.
It's cancer. You're trivializing the ultimate source of the problem. If we could ensure universal targeting of cancer cells, we wouldn't need a technically elaborate method of cellular death, like gene modification.
You might as well suggest solving world hunger by just feeding everyone.
No, I'm not. But it's occurred to me that I'm imagining this as treatment for Tasmanian devils that already have tumors. Maybe other people are envisioning it as a preventative measure.
And maybe that's part of the problem in trying to discuss it.
If the cells knew when they were supposed to die, then it wouldn't be cancer.
If the cure is telling the cells when they're supposed to die, then the cells that don't listen survive, ergo the cancer survives.
Which, in the sense of (non-preventitive) treatment, makes it a problem of universal targeting.