What Is Immunotherapy?

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Immunotherapy medicines use the power of your body’s immune system to attack cancer cells.

Your immune system is made up of a number of organs, tissues, and cells that work together to protect you from foreign invaders that can cause disease. When a disease- or infection-causing agent, such as a bacterium, virus, or fungus, gets into your body, your immune system reacts and works to kill the invaders. This self-defense system works to keep you from getting sick.

Cancer immunotherapy medicines work by helping your immune system work harder or more efficiently to fight cancer cells. Immunotherapy uses substances -- either made naturally by your body or man-made in a lab -- to boost the immune system to:

  • stop or slow cancer cell growth
  • stop cancer cells from spreading to other parts of the body
  • be better at killing cancer cells

To start an immune system response to a foreign invader, the immune system has to be able to tell the difference between cells or substances that are “self” (part of you) versus “non-self” (not part of you and possibly harmful). Your body’s cells have proteins on their surfaces or inside them that help the immune system recognize them as “self.” This is part of the reason the immune system usually doesn’t attack your body’s own tissues. (Autoimmune disorders happen when the immune system mistakenly attacks your own tissues, such as the thyroid gland, joints, connective tissue, or other organs.)

“Non-self” cells have proteins and other substances on their surfaces and inside them that the body doesn’t recognize, called antigens. Foreign antigens trigger the immune system to attack them and the cells they are in or on, whether viruses, bacteria, or infected cells. This response either destroys the foreign invaders or keeps them in check so they can’t harm the body.

So why doesn’t your immune system attack breast cancer cells on its own, without the help of immunotherapy medicines? There are two main reasons:

  • A breast cancer cell starts out as a normal, healthy cell. A cancerous growth is a collection of cells that were once normal and healthy. Precancerous and even early breast cancer cells don’t look that much different from normal cells. They don’t shout “non-self” in the way that bacteria, viruses, and other foreign materials do -- which makes things more challenging for the immune system. But as cells transform into cancer, they do create proteins that the immune system sees as “foreign” antigens. In some cases, the immune system is able to recognize some cancer cells as harmful and stop the process before a cancer can grow further.
  • As a cancer develops, the cancerous cells develop the ability to avoid the immune system. Breast cancer doesn’t happen overnight; it develops over a period of time. As healthy cells gradually change into cancer cells, the genetic information inside them is constantly changing. Some of these genetic changes allow the cancer cells to avoid detection by the immune system. Other changes allow cancer cells to speed up their growth rate and multiply much more quickly than normal cells do. This process can overwhelm the immune system and allow the breast cancer to grow unchecked.

In general, immunotherapy medicines can be divided into two main groups:

  • Active immunotherapies, which stimulate your immune system to respond to the cancer. Cells from a cancer are examined in the lab to find antigens specific to that tumor. Then an immunotherapy treatment is created that makes the immune system target those antigens. Cancer vaccines and adoptive cell therapy are examples of active immunotherapies.
  • Passive immunotherapies, which give the body man-made immune system components to help it fight cancer. Passive immunotherapies don’t stimulate your immune system to actively respond the way active immunotherapies do. Immune checkpoint inhibitors and cytokines are examples of passive immunotherapies.

Because immunotherapy medicines help your immune system to kill cancer, the process can take a long time. Right now, it’s not clear how long someone should be treated with immunotherapy. Many experts believe that combining immunotherapies, for example a vaccine with a checkpoint inhibitor, may be a good way to jump start a strong immune response to cancer. It’s also likely that immunotherapies will be combined with other cancer treatments, such as targeted therapies.

While there are many types of immunotherapies being studied, some of the most relevant to breast cancer treatment are:

  • cancer vaccines
  • adoptive cell therapy
  • immune checkpoint inhibitors
  • immune targeted therapies
  • cytokines

Right now, there are three targeted immunotherapies approved by the U.S. Food and Drug Administration (FDA) to treat breast cancer: Herceptin (chemical name: trastuzumab), Perjeta (chemical name: pertuzumab), and Kadcyla (chemical name: T-DM1 or ado-trastuzumab emtansine). These three medicines treat HER2-positive breast cancer by targeting the HER2 receptors on breast cancer cells.

Scientists are studying the immunogenicity of breast cancer -- how to provoke the immune system to respond to breast cancer -- as well specific immunotherapies. Stay tuned to Breastcancer.org for the latest updates.

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