Chemotherapy Principles

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What is chemotherapy?

The word chemotherapy means the use of any drug (such as aspirin or penicillin) to treat any disease, but to most people chemotherapy refers to drugs used for cancer treatment. It’s often shortened to “chemo.” Two other medical terms used to describe cancer chemotherapy are antineoplastic (meaning anti-cancer) therapy and cytotoxic (cell-killing) therapy.

History of chemotherapy

The first drug used for cancer chemotherapy did not start out as a medicine. Mustard gas was used as a chemical warfare agent during World War I and was studied further during World War II. During a military operation in World War II, a group of people were accidentally exposed to mustard gas and were later found to have very low white blood cell counts.

Doctors reasoned that something that damaged the rapidly growing white blood cells might have a similar effect on cancer. So, in the 1940s, several patients with advanced lymphomas (cancers of certain white blood cells) were given the drug by vein, rather than by breathing the irritating gas. Their improvement, although temporary, was remarkable.

That experience led researchers to look for other substances that might have similar effects against cancer. As a result, many other drugs have been developed.

Why chemotherapy is different from other treatments

Treatments like radiation and surgery are considered local treatments. They act only in one area of the body such as the breast, lung, or prostate and usually target the cancer directly. Chemotherapy differs from surgery or radiation in that it’s almost always used as a systemic treatment. This means the drugs travel throughout the body to reach cancer cells wherever they are. (There are ways to use chemotherapy to treat one part of the body. This is discussed in the section called “How is chemotherapy given?”)

Chemotherapy is used to treat many cancers. More than 100 chemotherapy drugs are used today — either alone or in combination with other drugs or treatments. As research continues, more drugs are expected to become available. These drugs vary widely in their chemical composition, how they are taken, their usefulness in treating specific forms of cancer, and their side effects.

New drugs are first developed through research in test tubes and animals. Then the drugs are tested in clinical trials in humans to find out how safe they are and how well they work.


Last Medical Review: 02/07/2013
Last Revised: 02/07/2013