Chemotherapy, << `kee` moh THEHR uh pee, >> is the treatment of cancers or infections with drugs that have a toxic effect on the cause of the illness. Ideally, chemotherapy is selectively toxic—that is, the drugs poison cancer cells or infectious microbes without harming healthy cells. Chemotherapy is most selectively toxic when it attacks diseases through a chemical step that does not occur in healthy cells. The antibiotic penicillin, for example, prevents certain bacteria from building their stiff cell walls. Animal cells do not form cell walls. This difference in chemistry makes penicillin selectively toxic to bacteria.
Cancer cells are chemically similar to the healthy cells from which they develop. This similarity makes it hard for scientists to create cancer drugs that are selectively toxic. Because cancer cells often divide more rapidly than normal cells, most cancer drugs attack cells as they divide. As a result, cancer drugs often kill rapidly dividing healthy cells, such as those that line the digestive tract and those that form hair. The death of normal cells causes nausea, hair loss, decreased immunity (resistance to disease), and other troublesome side effects. Doctors must supervise use of these drugs with great care.
