Understanding Chemotherapy

Approved by the Cancer.Net Editorial Board, 05/2018

Chemotherapy is the use of drugs to destroy cancer cells. It works by keeping the cancer cells from growing and dividing to make more cells. Because cancer cells usually grow and divide faster than normal cells, chemotherapy has a greater effect on cancer cells. However, the drugs used for chemotherapy are powerful, and they can still cause damage to healthy cells. This damage causes the side effects that are linked with chemotherapy.

Different types of chemotherapy

Treatment with these powerful drugs is called standard chemotherapy, traditional chemotherapy, or cytotoxic chemotherapy.

Several other types of drugs also treat cancer. Many of the newer drugs are called targeted drugs or targeted therapy. Targeted drugs damage cancer cells by blocking genes or proteins found in the cancer cells. Because these treatments work specifically on the cancer cells, they cause different side effects and usually damage healthy cells less. Other types of cancer therapy include hormones and drugs that work with your immune system to fight cancer, a type a treatment called immunotherapy.

How does chemotherapy treat cancer?

Doctors use chemotherapy in different ways at different times. These include:

  • Before surgery or radiation therapy to shrink tumors. This is called neoadjuvant chemotherapy.

  • After surgery or radiation therapy to kill any remaining cancer cells. This is called adjuvant chemotherapy.

  • As the only treatment. For example, to treat cancers of the blood or lymphatic system, such as leukemia and lymphoma.

  • For cancer that comes back after treatment, called recurrent cancer.

  • For cancer that spreads to other parts of the body, called metastatic cancer.

The goals of chemotherapy

The goals of chemotherapy depend on the type of cancer and how far it has spread. Sometimes, the goal of treatment is to get rid of all the cancer and keep it from coming back. If this is not possible, you might receive chemotherapy to delay or slow cancer growth.

Delaying or slowing cancer growth with chemotherapy also helps manage symptoms caused by the cancer. Chemotherapy given with the goal of delaying cancer growth is sometimes called palliative chemotherapy.

Your chemotherapy plan

There are many drugs available to treat cancer. A doctor who specializes in treating cancer with medication, called a medical oncologist, will prescribe your chemotherapy. You may receive a combination of drugs, because this sometimes works better than one drug alone.

The drugs, dose, and treatment schedule depend on many factors. These include:

  • The type of cancer

  • The tumor size, its location, and if or where it has spread. This is called the stage of cancer.

  • Your age and general health

  • How well you can cope with certain side effects

  • Any other medical conditions you have

  • Previous cancer treatments

Where is chemotherapy given?

Your health care team may give you chemotherapy at the clinic, doctor's office, or hospital. Some types of chemotherapy are given by mouth, and these can be taken at home.

How long does chemotherapy take?

Chemotherapy is often given for a specific time, such as 6 months or a year. Or you might received chemotherapy for as long as it works.

Side effects from many drugs are too severe to give treatment every day. Doctors usually give these drugs with breaks, so you have time to rest and recover before the next treatment. This lets your healthy cells heal.

For example, you might get a dose of chemotherapy on the first day and then have 3 weeks of recovery time before repeating the treatment. Each 3-week period is called a treatment cycle. Several cycles make up a course of chemotherapy. A course usually lasts 3 months or more.

Some cancers are treated with less recovery time between cycles. They call this a dose-dense schedule. It can make chemotherapy more effective against some cancers. But it also increases the risk of side effects. Talk with your health care team about the best schedule for you.

How is chemotherapy given?

Intravenous (IV) chemotherapy. Many drugs require injection directly into a vein. This is called intravenous or IV chemotherapy. Treatment takes a few minutes to a few hours. Some IV drugs work better if you get them over a few days or weeks. You take them through a small pump you wear or carry. This is called continuous infusion chemotherapy.

Oral chemotherapy. You can take some drugs by mouth. They can be in a pill, capsule, or liquid. This means that you may be able to pick up your medication at the pharmacy and take it at home. Oral treatment for cancer is now more common, since many drugs used for targeted therapy work this way. Some of these drugs are given daily, and others are given less often. For example, a drug may be given daily for 4 weeks followed by a 2-week break.

Injected chemotherapy. This is when you receive chemotherapy as a shot. In some cases, the shot is given in a muscle, while other drugs are injected under the skin. This could be in the arm, leg, or abdomen.

Chemotherapy into an artery. An artery is a blood vessel that carries blood from your heart to another part of your body. Sometimes chemotherapy is injected into an artery that goes directly to the cancer. This is called intra-arterial or IA chemotherapy.

Chemotherapy into the peritoneum or abdomen. For some cancers, medication might be placed directly in your abdomen. Abdomen is the medical term for your belly. This type of treatment works for cancers involving the peritoneum. The peritoneum covers the surface of the inside of the abdomen and surrounds the intestines, liver, and stomach. Ovarian cancer is one type of cancer that frequently spreads to the peritoneum.

Topical chemotherapy. You can take some types of chemotherapy in a cream you put on your skin. You get your medication at the pharmacy and take it at home.

Other drug treatments for cancer

The traditional drugs used for chemotherapy are an important part of treatment for many cancers. The drugs affect both cancer cells and healthy cells. But scientists have designed newer drugs that work more specifically to treat cancer. These treatments cause different side effects.

Doctors may use these newer cancer drugs as the only drug treatment. But they are usually added to traditional chemotherapy. These types of treatment include:

Hormone therapy. These treatments change the amount of hormones in your body. Hormones are chemicals your body makes naturally. They help control the activity of certain cells or organs. Doctors use hormone therapy because hormone levels control several types of cancers. This includes some breast and prostate cancers.

Targeted therapy. These treatments target and disable genes or proteins found in cancer cells that the cancer cells need to grow.

Immunotherapy. This type of treatment helps your body's natural defenses fight the cancer. This type of treatment may be used for some types of cancer now and will play an increasingly important role in cancer treatment in the future. 

Related Resources

What to Expect When Having Chemotherapy

Catheters and Ports in Cancer Treatment

Making Decisions About Cancer Treatment

More Information

Chemocare.com: What is Chemotherapy?

National Cancer Institute: Chemotherapy to Treat Cancer

ASCO answers; Understanding Chemotherapy

Download ASCO's free 1-page fact sheets on Understanding Chemotherapy and Oral Chemotherapy. These printable PDFs provide an introduction to chemotherapy, answers to common questions, terms to know, and questions to ask the doctor. Order printed copies of both fact sheets from the ASCO University Bookstore.