How do radiation and chemotherapy affect cancer cells?

To start with there are over 100 different medications/drugs under the general term
"chemotherapy." These drugs have different mechanisms of action – different ways that they affect cancer cells. In general, most of these drugs damage the DNA molecules in cancer cells and normal body cells. That is how radiation works also – damaging the DNA molecules in the chromosomes of cancer cells and normal cells. Damage to the DNA by some chemotherapy drugs and from Radiation makes the cells affected unable to divide and reproduce themselves. This causes the death of the cancer cells affected by the treatment. The problem over the past 50 years has been trying to kill just the cancer cells and not hurt normal cells. This is very difficult because there are few differences between cancer cells and normal cells that we can exploit.