This is the first article in a three-part series, and it provides an overview of the basics of chemotherapy. Other articles in this series address what to expect when receiving chemotherapy and side effects of the treatment.

Chemotherapy is the use of drugs to kill cancer cells. A doctor who specializes in treating cancer with medication is called a medical oncologist. Some people may receive chemotherapy in their doctor's office, at an outpatient clinic, or at the hospital; others may take the medicine at home, depending on the type of chemotherapy. A chemotherapy regimen (schedule) usually consists of a specific number of cycles given over a specific time.

Unlike radiation therapy and surgery, chemotherapy is a systemic treatment, which means that it is delivered through the bloodstream to target cancer cells throughout the body. Chemotherapy targets cells that are actively growing because uncontrolled growth is one of the characteristics of cancer cells. However, such drugs cannot differentiate between normal cells that are reproducing and cancerous cells; side effects occur when the drugs damage normal cells.

Uses of chemotherapy

Chemotherapy is commonly used as an adjuvant treatment (treatment given after the main treatment, such as surgery or radiation therapy) to kill any cancer cells that remain. It may also be used as neoadjuvant therapy (treatment given before surgery or radiation therapy to shrink tumors). Finally, chemotherapy is used to treat recurrent cancer (cancer that comes back after treatment) or metastatic cancer (cancer that has spread to other parts of the body).

Goals of chemotherapy

The primary goal of chemotherapy is to eliminate the cancer cells and prevent recurrence (having the cancer come back after treatment). If it is not possible to eliminate the cancer, chemotherapy may be used to control the cancer by slowing its growth and/or to reduce symptoms caused by the cancer (called palliative therapy). Learn more about palliative care.

The chemotherapy treatment plan

More than 100 drugs are available to treat cancer. Often, oncologists will combine drugs to more effectively treat a patient's cancer.

The drug or combination of drugs—as well as the dose and treatment schedule—that the doctor recommends depends on many factors, including the type and stage (describes the size and location of the tumor and whether it has spread) of cancer; the patient's overall health, age, and tolerance of certain side effects; the presence of other medical conditions; and previous cancer treatments.

Most people receive chemotherapy in periods of treatment followed by periods of recovery, which allow noncancerous cells time to heal. For example, a patient may receive one week of treatment followed by three weeks of recovery. Several of these cycles complete a course of chemotherapy, which generally lasts three months or longer. For some cancers, it may be beneficial to use a dose-dense schedule, meaning that there is less recovery time between treatment cycles. This can slightly improve the effectiveness of the chemotherapy, but it increases the risk of side effects. Patients may consider discussing this schedule with their doctors.

Ways of receiving chemotherapy

Intravenously (IV). The medication goes directly into a vein. It is the most common method of chemotherapy administration (process of giving medication). A dose of IV chemotherapy usually lasts a few minutes to a few hours; however, a few drugs are more effective when given at a slow continuous rate for a few days or for weeks at a time.

Orally. The medicine is taken through the mouth and swallowed as a pill, capsule, or liquid.

As an injection. The medicine is given as a shot to a muscle or to the fatty part of the arm, leg, or abdomen.

Intra-arterially (IA). The medicine goes directly into the artery that is supplying blood to the cancer.

Intraperitoneally. The medicine goes directly into the abdomen or peritoneal cavity (the part of the body that contains the intestines, liver, stomach, and—in women—ovaries).

Topically. The medicine is applied as a cream, rubbed into the skin.

Types of chemotherapy

Systemic cancer treatments work by interfering in various ways with cancer cell growth and division. Traditional chemotherapy drugs interfere with processes that are similar in cancer cells and normal cells, such as making proteins or dividing into new cells. Meanwhile, some of the newer therapies affect cancer cells by targeting processes that are vital to the cancer cell but not important to normal cells. These newer therapies have different (and usually fewer) side effects and can be used either alone or in combination with traditional chemotherapy.

Hormone therapy. These treatments change the amount of hormones (natural chemicals that circulate in the bloodstream and regulate the activity of certain cells or organs) in the body, which helps because several types of cancer—including some breast and prostate cancers—can only grow and spread in the presence of certain hormones.

Targeted therapy. These treatments target specific genes or proteins within the cancer cell or affect the tissue environment that contributes to cancer growth and survival. Learn more about targeted treatments.

Immunotherapy. These treatments are designed to boost the body's natural defenses to fight the cancer. It uses materials made either by the body or in a laboratory to bolster, target, or restore immune system function. Learn more about immunotherapy.

More Information

Types of Treatment

Additional Resources

National Cancer Institute: Questions and Answers About Chemotherapy

Chemocare.com: What is Chemotherapy?

Last Updated: November 29, 2010