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The Immune System's Role in Cancer

Instructor: Sarah Friedl

Sarah has two Master's, one in Zoology and one in GIS, a Bachelor's in Biology, and has taught college level Physical Science and Biology.

Your immune system's job is to protect you from a lot of harmful stuff, including cancer. But when our immune system isn't enough, treatments such as chemotherapy and immunotherapy may help.

Your Immune System

Your immune system is your body's first line of defense against the world around it. No matter how hard you try, you can't avoid germs, viruses, harmful bacteria, and other pathogens that are trying to invade your body. Most of the time you don't even know this is happening - those foreign invaders are so small you can't see them! Your immune system is also designed to attack those invaders before they make you sick. That way, you can go about your business without skipping a beat.

Cancer cells grow uncontrolled
cancer cells

One of the most important things that our immune system can protect us from is cancer. Cancers occur in the body when cell growth goes haywire. The cancer cells divide, and divide, grow, and spread, and eventually kill the host, which is the person with cancer. These cancer cells are not normal cells, so our immune system sees them as 'invaders' and attacks them before they grow too large and cause problems.

And this is actually occurring more often than you realize. Cancer cells are developing all the time, but your immune system is destroying them before they get out of control. Think about it: with almost 40 trillion cells in your body, there's a good chance that at least a few of them will get out of control and need to be 'terminated' by your immune system. And this is what your immune system does - it seeks and destroys those cells!

A cancer cell being attacked
attack on cancer

Cancers Can Evade the Immune System

But sometimes our immune system fails us. This can happen for a number of reasons. Perhaps our immune system is weakened and is not strong enough to fight the cancer. Other times, the cancer cells may have proteins on them that causes the attacking immune system cells to become inactive. If your immune cells are like an army attacking the cancer cells, this would be like the cancer cells throwing out some tear gas to neutralize the oncoming soldiers. Some cancer cells may even be able to recruit other cells in the surrounding area to suppress immune system activity as well. Now that's clever!

Cancer cells can also be quite sneaky. Antigens are substances on foreign invaders that signal your immune system to attack. They are like a big sign that reads 'I DON'T BELONG HERE!' and your immune cells respond accordingly. But cancer cells are sometimes able to reduce the expression of those antigens, making that sign smaller and more difficult for the immune cells to see.

Cancer Treatments Weaken the Immune System

While cancer itself can weaken the immune system, treatments for cancer can also have serious effects on your immune health. Chemotherapy is one such treatment, where drugs are given to the person with cancer to disrupt steps of the cell cycle, which is where the cancer cells are allowed to grow and divide uncontrollably.

One of the side effects of chemotherapy is hair loss
chemotherapy

But because immune cells also go through the cell cycle, chemotherapy can also have a negative effect on their production. This leaves you at greater risk for infection and other microscopic pathogen attacks. This is in addition to the other common side effects of chemotherapy treatment such as severe nausea, hair loss, and weight loss.

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