Cancer Vaccines

This information was reprinted with permission. © 2008 American Society of Clinical Oncology. All rights reserved. www.Cancer.net 11/18/08

A vaccine helps the body fight disease. Most people are familiar with vaccines for diseases like chicken pox or the flu. Vaccines (sometimes called vaccinations) help train the immune system to recognize and destroy harmful substances, such as bacteria or viruses, before they can cause disease.

There are two types of cancer vaccines: prevention vaccines and treatment vaccines. A prevention vaccine is given to a healthy person to prevent the development of a specific type of cancer. The U.S. Food and Drug Administration (FDA) has approved two vaccines for cancer prevention. Gardasil is a vaccine that prevents infection with the human papilloma virus (HPV). A long-lasting infection with HPV can cause cervical cancer. (HPV is also thought to cause other types of cancer, but so far, the vaccine is only approved for cervical cancer.) The other approved vaccine prevents infection with the hepatitis B virus (HBV); long-term infection with HBV can lead to the development of liver cancer.

A cancer treatment vaccine is a type of biologic therapy. Biologic therapy, also called immunotherapy, helps the body's immune system fight the cancer. A treatment vaccine may prevent cancer from coming back, destroy any remaining cancer cells after other types of treatment, or stop cancer cell growth. A cancer vaccine is designed to be specific, which means it is supposed to get rid of the cancerous cells and not the healthy cells. Vaccines for cancer treatment are still in development and only available through a clinical trial (research study involving people).

How a cancer vaccine works

The task of a person's immune system is to tell the difference between something that is part of the body and a substance that is potentially harmful to the body, such as a virus. This identification is made through antigens, which are substances on the surface of cells that are not normally part of the body. The immune system recognizes the antigens and attacks them, typically eliminating them. Some immune system cells release specialized proteins called antibodies that help destroy the antigens. Other immune system cells may attack antigens directly, without the help of antibodies. The immune system is left with a "memory" that helps it respond to those antigens in the future.

A cancer vaccine takes advantage of the immune system's response to antigens. Often, cancer cells have specific molecules or more numerous ones that are not present on healthy cells. When injected into a person, these specific molecules act as antigens, which stimulate the immune system to recognize and destroy cancer cells with these antigens. Most cancer vaccines also contain adjuvants, substances that may help improve the immune response.

There are two sources of antigens: those made from a patient's cells and those from cells or proteins that are developed in a laboratory. A vaccine that is customized for each patient may be more effective because the antigens are specific to the patient's tumor. However, they are also more expensive. A vaccine made in the laboratory may not be as specific for an individual patient, but are somewhat less expensive and may be easier to make.

Successes and challenges of cancer vaccines

In clinical trials of cancer vaccines, doctors have seen few side effects. The most common one is skin irritation at the place where the needle is injected. Also, patients who receive the vaccine produce the expected immune system response. However, when the cancer vaccines are tested in phase III clinical trials (the point at which a vaccine is tested against the best standard treatment), there hasn't been an improvement in survival. Some of the reason for this may be:

  • Cancer cells suppress the immune system-this is how the cancer is able to grow and develop in the first place. An adjuvant may help overcome this problem.
  • The immune system doesn't always recognize that cancer cells are harmful. Because cancer cells develop from a person's own healthy cells, they may not "look" harmful to the immune system. Instead of being eliminated, the cancer cells are ignored.
  • Larger or more advanced tumors are hard to destroy, especially with only a vaccine. This is a reason why cancer vaccines are given in addition to other treatments.
  • The immune systems of people who are sick may not be able to produce a good immune response. Also, a person's immune system slows with age, limiting the effectiveness of the vaccine.

Because of these reasons, some researchers think that a cancer treatment vaccine may be more effective in patients with smaller tumors or early-stage cancers.

Vaccines and clinical trials

Several vaccines are being tested in clinical trials. According to the National Cancer Institute (NCI), vaccines for melanoma (both skin and ocular [eye]), leukemia, non-Hodgkin lymphoma, multiple myeloma, brain tumors, kidney cancer, lung cancer, pancreatic cancer, and prostate cancer are being evaluated in phase III clinical trials. Usually, these vaccines are given in addition to other treatment, such as chemotherapy.

Clinical trials are important for learning more about cancer vaccines. Talk with your doctor about the possibility of a cancer vaccine clinical trial. Some questions to ask the doctor include:

  • What is the vaccine and how does it work?
  • How is this vaccine made?
  • How often is the vaccine given?
  • How long will I need the vaccine?
  • What are the possible side effects?
  • Is there another treatment option for this cancer?
  • Is there anything else I need to know?

Although vaccines for treating cancer seem promising, they are still considered investigational treatments. More research is needed to understand how the immune system can be trained to recognize and eliminate cancer cells.