As opposed to tainted electricity? Sorry. Couldn't resist. A cancer cell is exactly like a healthy cell, except it reproduces uncontrollably, sapping the energy from the cells around it, which kills them. Basically, the only difference between a cancerous cell and a healthy one is a very VERY tiny DNA discrepancy. Any electricity that would kill this cancer cell would also kill any healthy one it passes through. This is why we use radioactivity. It's much easier to focus the radiation on a single affected area. To "zap" a cancer cell and kill it outright means pumping the same amount of deadly power to every cell between the anode and the cancer, and then again from the cancer cell to the cathode. You'd burn a hole in the body. Not to me tion the most likely lethal amounts of electricity getting shoved into the body.