The immune system and cancer

This page is about the immune system. It also tells you about the effects that cancer or treatments may have on the immune system. Some treatments can boost the immune system to help fight cancer. There is information about 

What the immune system does

The immune system protects the body against illness and infection caused by bacteria, viruses, fungi or parasites. It is really a collection of reactions and responses that the body makes to damaged cells or infection. So it is sometimes called the immune response.

The immune system is important to cancer patients in many ways because

  • Cancer can weaken the immune system
  • Cancer treatments may weaken the immune system
  • The immune system may help to fight cancer

Cancer and treatments may weaken immunity

Cancer can weaken the immune system by spreading into the bone marrow. The bone marrow makes blood cells that help to fight infection. Weakening of the immune system happens most often in leukaemia or lymphoma. But it can happen with other cancers too. The cancer in the bone marrow stops the bone marrow making so many blood cells.

Chemotherapy, biological therapies and radiotherapy can temporarily weaken immunity by causing a drop in the number of white blood cells made in the bone marrow. High doses of steroids can also weaken your immune system while you are taking them.

You can find information about the different types of cancer treatments.

The immune system can help to fight cancer

Some cells of the immune system can recognise cancer cells as abnormal and kill them. Unfortunately, this may not be enough to get rid of a cancer altogether. But some new treatments aim to use the immune system to fight cancer.

There are two main parts of the immune system

  • The inbuilt protection we have from birth
  • The immune protection we develop from being exposed to certain diseases

In built immune protection

This is also called innate immunity. These immune mechanisms are always ready and prepared to defend the body from infection. They can act immediately (or very quickly). This in built protection comes from

  • A barrier formed by the skin around the body
  • The inner linings of the gut and lungs, which produce mucus and trap invading bacteria
  • Hairs that move the mucus and trapped bacteria out of the lungs
  • Stomach acid, which kills bacteria that have been swallowed
  • Helpful bacteria growing in the bowel, which prevent other bacteria from taking over
  • Urine flow, which flushes bacteria out of the bladder and urethra
  • White blood cells called neutrophils, which can find and kill bacteria and other infectious organisms

There are several ways that these natural protection mechanisms can be damaged or overcome if you have cancer. For example

  • Something may break the skin barrier, such as having a drip in your arm or a wound from surgery
  • Chemotherapy may damage to the lining of the gut – for example, severe diarrhoea caused by some chemotherapy drugs can break down the gut lining
  • A catheter into your bladder can become a route for bacteria to get inside the bladder and cause infection
  • Radiotherapy to the lung can damage the hairs and mucus producing cells that help to remove bacteria
  • Anti acid medicines for heartburn may neutralise the stomach acid that kills bacteria
  • Chemotherapy can temporarily reduce the number of neutrophils in the blood (the neutrophil count) which means it is more difficult for you to fight off infection


These white blood cells are very important for fighting infection. They can

  • Move to areas of infection in the body
  • Stick to the invading bacteria, viruses or fungi
  • Swallow up the bacteria, viruses or fungi and kill them with chemicals

Your normal neutrophil count is between 2,000 and 7,500 per cubic millimetre of blood. When you don't have enough neutrophils you are said to be neutropaenic.

Chemotherapy and some radiotherapy treatments can lower the neutrophil count. So, after chemotherapy, biological therapy and some types of radiotherapy you may be more likely to get bacterial or fungal infections.

If you are having cancer treatment, it is important for you to know that

  • Infections can become serious very quickly in people with low neutrophil counts
  • Antibiotics could save your life, so if you get a fever or feel ill, phone your cancer centre or go to Accident and Emergency (A&E) straight away

You are more likely to become ill from bugs you carry around with you normally, not from catching someone else's. This means that you usually don't have to avoid your family, friends or children when you go home after chemotherapy.

You can ask your cancer doctor or nurse what precautions you should take against infection. 

When your blood counts are low, you may need to take antibiotics to help prevent severe infection.

Acquired immunity

This is immune protection that the body learns from being exposed to diseases. The body learns to recognise each different kind of bacteria, fungus or virus it meets for the first time. The next time that particular bug tries to invade the body, the immune system is ready for it and able to fight it off more easily. This is why you usually only get some infectious diseases once – for example, measles or chicken pox.

Vaccination works by using this type of immunity. A vaccine contains a small amount of protein from a disease. This is not harmful, but it allows the immune system to recognise the disease if it meets it again. The immune response can then stop you getting the disease. Some vaccines use tiny amounts of the live bacteria or virus. These are called live attenuated vaccines. 

Attenuated means that the virus or bacteria has been changed so that it will stimulate the immune system to make antibodies but won't cause the infection. Other types of vaccine use killed bacteria or viruses, or parts of proteins produced by bacteria and viruses.

B cells and T cells

The white blood cells involved in the acquired immune response are called lymphocytes. There are two main types of lymphocytes – B cells and T cells. B and T lymphocytes are made in the bone marrow, like the other blood cells. 

Lymphocytes have to fully mature before they can help in the immune response. B cells mature in the bone marrow. But the immature T cells travel through the bloodstream to the thymus gland where they become fully developed.

Once they are fully mature, the B and T cells travel to the spleen and lymph nodes ready to fight infection.

You can read about the thymus, spleen and lymph nodes on our page about the lymphatic system and cancer.

What B cells do

B cells react against invading bacteria or viruses by making proteins called antibodies. The antibody made is different for each different type of germ (bug). The antibody locks onto the surface of the invading bacteria or virus. The invader is then marked with the antibody so that the body knows it is dangerous and it can be killed off. Antibodies can also detect and kill damaged cells.

The B cells are part of the memory of the immune system. The next time the same germ tries to invade, the B cells that make the right antibody are ready for it. They are able to make their antibody very quickly.

How antibodies work

Antibodies have two ends. One end sticks to proteins on the outside of white blood cells. The other end sticks to the germ or damaged cell and helps to kill it. The end of the antibody that sticks to the white blood cell is always the same. So it is called the constant end.

The end of the antibody that recognises germs and damaged cells varies depending on the cell it is designed to recognise. So it is called the variable end. Each B cell makes antibodies with a different variable end from other B cells.

Cancer cells are not normal cells. So some antibodies with variable ends recognise cancer cells and stick to them.

What T cells do

There are different kinds of T cells called

  • Helper T cells
  • Killer T cells

The helper T cells stimulate the B cells to make antibodies, and help killer cells develop.

Killer T cells kill the body's own cells that have been invaded by the viruses or bacteria. This prevents the germ from reproducing in the cell and then infecting other cells.

Cancer treatments that use the immune system

Some cancer treatments use elements of the immune system to help treat cancer.


Immunotherapy is a type of biological therapy. Biological therapies use natural body substances or drugs made from natural body substances to treat cancer. Immunotherapies are treatments that use your immune system. They are helpful in cancer treatment because cancer cells are different from normal cells and so can be picked up by the immune system.

Many different chemicals produced as part of the immune response can now be made in the laboratory. These include interferon, interleukin 2 and monoclonal antibodies.

Interferon alpha and interleukin 2 act by boosting the immune response to help the body kill off cancer cells.

Scientists are also trying to develop vaccinations against cancer cells. It may be possible for the vaccine to train the immune system to see cancer cells as being invaders and kill them.

You can read more about biological therapies.

Monoclonal antibodies

Monoclonal antibodies are made in the laboratory. The scientists developing them make an antibody with a variable end that recognises cancer cells. Monoclonal means that all the antibodies are exactly the same type, with the same variable end.

The monoclonal antibodies recognise molecules on the outside of cancer cells. Different antibodies have to be made for different types of cancer, for example

  • The drug Rituximab (Mabthera) recognises CD20 protein on the outside of some lymphoma cells
  • Bevacizumab (Avastin) targets growth factors that help blood vessels grow and is used to treat bowel cancer, breast cancer and some other cancers
  • Trastuzumab (Herceptin) recognises breast cancer cells that produce too much of the protein HER 2

The constant end of cancer treating monoclonal antibodies kills the cancer cells by marking them so that other immune system cells pick them out. The job of these other cells is to find antibody labelled cells and kill them.

Scientists can sometimes make the monoclonal antibody even better at killing cancer cells. They may attach a radioactive atom that delivers radiation directly to the cancer cells. Or they can attach a chemotherapy drug that is taken straight to the cancer cells by the monoclonal antibody.

Monoclonal antibodies are used for many types of cancer. You can find out more about monoclonal antibodies.

There is a lot of research going on into using immune system therapies to treat cancer. You can find information about monoclonal antibody trials on our clinical trials database.

Stress, the immune system and cancer

Many people with cancer believe that they should strengthen their immune systems to help beat the disease. There is a commonly held belief that reducing stress can help to strengthen our immune systems. This is the thinking behind some complementary therapies, such as using relaxation techniques.

There is some scientific evidence that stress weakens our immunity. Two studies looking at whether stress affected cancer recurrence had conflicting results. While no one knows whether strengthening immunity can help to cure cancer, most doctors and nurses agree that reducing stress is a good thing to do.

While many life stresses cannot be avoided altogether, there are ways you can try to help yourself. Many complementary therapies such as meditation, massage and reflexology, can be very relaxing.

You can avoid getting run down and look after yourself by

  • Eating a balanced diet when you are able
  • Trying to eat fresh food whenever possible
  • Getting plenty of rest – even if you find it hard to sleep, you can rest
  • Doing gentle exercise if you are able

You can find out about complementary therapies.

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