Drug therapy, also called chemotherapy, is used against a wide variety of cancers. Chemotherapy has proved especially effective in treating leukemia, lymphoma, and testicular cancer. Cancer cells divide much more rapidly than normal cells. Therefore, many cancer drugs are designed to interfere with cell division.

Chemotherapy causes side effects by injuring the normal body cells, especially those that divide most rapidly. Rapidly dividing normal cells include blood-forming cells, cells that line the intestines, and hair-forming cells. Damage to blood-forming cells may increase a patient's risk of developing anemia or an infection. Injury to intestinal cells may cause nausea and vomiting. Disruption of hair-forming cells can cause hair loss. Researchers work constantly to develop drugs that reduce harm to normal cells.

Effective chemotherapy usually involves combinations of drugs. Doctors combine drugs that have different methods of acting on cancer cells and that produce different side effects. Combination therapy reduces the chance that cancer cells will develop resistance to the drugs. It also helps avoid serious side effects from large doses of a single drug.