From Wikipedia:
Although dichloroacetate "has actually been used safely in humans for decades" its therapeutic use can cause pain, numbness and gait disturbances in some patients.
http://en.wikipedia.org/wiki/Dichloroacetic_acid
Interesting that it says TINY doses work. Perhaps that would reduce the side effects. However, the side effects, if self-limiting in duration, are a small price to pay to kill the cancer cells.