Well, killing 99% of cancer cells is quite useless, the 1% left will now thrive and if they survived because they were different (and not just luckily escaping the treatment) you now have 100% of cancer cells you can't treat anymore.
Better case, the 1% "lucky" cancer cells just re-invade.
I can destroy 99% of cancer cells in a lab using a hammer. The important part is whether you can do the same in a person without killing them.
Well, killing 99% of cancer cells is quite useless, the 1% left will now thrive and if they survived because they were different (and not just luckily escaping the treatment) you now have 100% of cancer cells you can't treat anymore.
Better case, the 1% "lucky" cancer cells just re-invade.
It could extend the life of the patient with a few years.
Maybe, or just extending the suffering for a couple of months. Hope it gets better!