The use of chemicals (drugs or medications) to kill malignant cells. Numerous chemicals have been developed for this purpose, and most act to injure the DNA of the cancer cells. When the DNA is injured, the cells cannot grow or survive. Successful chemotherapy depends on the fact that malignant cells are somewhat more sensitive to the chemicals than normal cells. Because the cells of the marrow, the intestinal tract, the skin and the hair follicles are particularly sensitive to these chemicals as well, injury to these organs causes the common side effects of chemotherapy: mouth sores and hair loss.

Physicians generally use combinations of several drugs to kill malignant cells. Combining drugs that have different mechanisms of action helps prevent drug resistance. Combination therapy is usually given in cycles that last for three to four weeks. Some drugs are given continuously for several days, while others are used in an interrupted fashion for only a few days during the cycle. Two different drug combinations are sometimes administered in alternate cycles. Decisions as to the type of therapy to use are based on the duration of the drug's effect, the patient's tolerance of the drug and the maintenance of adequate levels of the drug in blood or tissues. Treatment may consist of six or more cycles, lasting from four to 12 months. Chemotherapy drugs are dissolved in fluid and usually administered to the patient through a peripheral intravenous (IV) line. It is possible that a port, a central line or a percutaneously inserted central venous catheter'known as a "PICC" or "PIC" line'may be used for some patients.