Actually, that was its downfall. That it did not completely eliminate the cancer cells.
The concept was, that cancer cells tend to clump, and grow abnormally, with much of their metabolism given over to reproduction -- under that circumstance, they should be susceptible to heat stress, dying readily when exposed to even mild amounts of it. One could elevate the body temperature, or isolate the tumor and raise the temperature locally. Many cancer cells could be expected to succumb to this ordeal, but unfortunately not all.
Those tumor cells on the periphery were hardly affected at all, and of course they resumed their destructive growth as soon as the heat regimen was removed.
ah.