Health A-Z

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Harvard Medical School

Chemotherapy

What Is It?

Chemotherapy drugs are medicines used to kill cancer cells, shrink tumors and possibly prevent cancer from spreading. These drugs are also called anti-cancer drugs or chemotherapeutic agents. There are more than 80 anti-cancer drugs available, with many more being studied. Each type of anti-cancer drug works in a slightly different way. In general, they all kill cancer cells, or interfere with the ability of cancer cells to divide and grow, which can limit the size of cancerous tumors. In killing cancer cells, the use of chemotherapy also may prevent cancer from spreading (metastasizing) to other parts of the body, such as to the bone, brain, liver or lungs.

Anti-cancer drugs come in many different combinations, and specialists called oncologists who use them follow many different treatment schedules. Because of the many ways cancer cells grow, the use of combinations of chemotherapy drugs (rather than a single drug) have been shown to be more effective, as the combinations can result in more-effective elimination of the cancer cells. Each person's chemotherapy plan depends on the cancer being treated and how far the cancer has spread.

Chemotherapy is generally given by administering the drugs through a vein, as most people receive anti-cancer drugs through a process called intravenous infusion. A bag filled with the liquid drug is attached to a tube that is inserted into a vein. The drug slowly drips into the patient's body. Other people get their anti-cancer drugs from injections or in pill form.

Chemotherapy drugs reach almost all parts of the body. This is called systemic therapy, since the chemotherapy may eliminate the presence of microscopic cancer cells that have not yet become large enough for physicians to detect through the use of x-rays or other diagnostic testing. Administering the chemotherapy through the vein helps to kill cancer cells that have spread from the original site of the cancer. Because of the structure of the brain and the testes, often chemotherapy may not necessarily penetrate into these tissues. Frequently treatment programs may use additional methods to attempt to eliminate the cancer cells that may be present in these two areas, since the brain and the testes usually are exposed only to very low concentrations of chemotherapy drugs. Cancers in these areas may be treated differently.

Unfortunately, cancer chemotherapy agents are not specific for cancer cells. This means that anti-cancer drugs attack more than just cancer cells. Normal, healthy cells are destroyed as well, especially cells lining the mouth, digestive tract, and hair follicles and the blood cells within bone marrow. This is why many people receiving chemotherapy get mouth sores and upset stomachs, lose their hair, and feel weak. A common side effect of chemotherapy is increased susceptibility to infections because the chemotherapy knocks down the production of new blood cells in the bone marrow. When white cell counts get too low, the body loses the ability to fight bacteria, viruses and other germs. These infections can be very serious and often require hospitalization. The risk of infection lessens when the white blood counts recover.

The bone marrow also produces specialized cells that are required for blood clotting. Chemotherapy can also affect these cells, leading to an increased risk of bleeding. The cells involved are called platelets. As the effects of chemotherapy wear off on the bone marrow, the risk of bleeding also diminishes.