Cytotoxic: Literally, “toxic to cells.” Anything that kills cells outright could be called cytotoxic. In terms of cancer, you will usually hear this word in connection to chemotherapy and radiation, and even some supplements. That’s because these treatments directly kill cells; cancer cells, but also other living cells. Veterinary oncologists are very aware of the cytotoxic effects of these treatments, and try hard to balance killing cancer cells with killing normal, healthy cells. This is why these treatments aren’t usually given at the maximum tolerated dose in dogs. Giving dogs a “killing” dose might kill the cancer, but it might also cause side effects that no one wants for a dog.