Theoretically, those cancers that are dividing more rapidly than normal cells will be killed before the patient is, but it is nip and tuck all the way. In the case of a cancer that is dividing at the same rate or even slower than normal cells, there isn't even a theoretical chance of success. In either event, poisoning the system is the objective of these drugs, and the resulting pain and illness often is a torment worse than the disease itself. The toxins catch the blood cells in the act of dividing and cause blood poisoning. The gastrointestinal system is thrown into convulsion causing nausea, diarrhea, loss of appetite, cramps, and progressive weakness.
Hair cells are fast-growing, so the hair falls out during treatment.
Reproductive organs are affected causing sterility. The brain becomes fatigued. Eyesight and hearing are impaired. Every conceivable function is disrupted with such agony for the patient that many of them elect to die of the cancer rather than to continue treatment. It is ironic that the personnel who administer these drugs to cancer patients take great precautions to be sure they themselves are not exposed to them.