Immunotherapy

Immunotherapy is treatment that uses certain parts of a person’s immune system to fight diseases such as cancer. Different types of immunotherapy drugs are available, and they work in different ways. 

Immunotherapy can work by stimulating the immune system to find cancer cells or by adding components to a person’s immune system such as man-made immune system proteins. 

Clinical trials are underway in triple negative breast cancer and HER2-positive breast cancer to test the effectiveness of immunotherapy drugs.

The immune system 

Our immune system is made up of white blood cells, lymph glands and organs, such as the spleen, that protect us from disease.  

Two main types of white blood cells (called lymphocytes) are in the immune system: 

• B cells that fight bacteria or viruses by making proteins called antibodies 
• T cells that recognise unfamiliar substances, germs and abnormal cells, like cancer cells, and trigger an immune response to fight infection and illness. T cells also help the B cells to make antibodies. 

The immune system usually prevents cancer from developing by detecting and destroying abnormal cell growth. Sometimes the body’s immune system is not strong enough to stop cancer from developing.

Immunotherapy 

Immunotherapy, sometimes called biological or biologic therapy, is a type of cancer treatment that works by boosting the person’s immune system to fight diseases such as cancer. Immunotherapy typically works on specific proteins involved in the immune system to enhance the immune response.  

Types of immunotherapies include:  

• Monoclonal antibodies – work in more than one way to control cancer cells. Also referred to as targeted therapy because they block a specific protein on the cancer cell to keep it from growing.  
• Checkpoint inhibitors – block proteins that stop the immune system from attacking cancer cells.  
• Cancer vaccines – help the body prevent some types of cancer caused by infections or help the body fight cancer. This treatment is not currently available for breast cancer.

How it works 

How does immunotherapy work in breast cancer?

An important part of the immune system is its ability to keep itself from attacking normal cells in the body. To do this, it uses proteins (or "checkpoints") on immune cells (T cells) that need to be turned on (or off) to start an immune response. Breast cancer cells sometimes use these checkpoints to avoid being attacked by the immune system.

There are drugs that block different checkpoint proteins, including: 

• PD-1 (programmed cell death protein 1), e.g. pembrolizumab.    
• PD-L1 (programmed cell death ligand 1), e.g. durvalumab 
• CTLA-4 (cytotoxic T lymphocyte associated protein 4), e.g. tremelimumab. 

PD-1 and CTLA-4 are found on T cells, and PD-L1 is found on cancer cells.  

PD-1 helps to prevent T cells from attacking other cells in the body (like an “off” switch) by binding to PD-L1, a protein on some normal (and cancer) cells. Some cancer cells have high levels of PD-L1, which helps them hide from the immune system.  

CTLA-4 is another checkpoint protein on some T cells that acts as a type of “off” switch to help keep the immune system in check. 

Checkpoint inhibitors are drugs designed to block these checkpoint proteins to enable the T cells to recognise and destroy cancer cells. Checkpoint inhibitors are a type of immunotherapy being studied in clinical trials for the treatment of breast cancer.

Checkpoint inhibitors

Side effects 

Side effects of immunotherapies may include: 

• Fatigue (tiredness) 
• Dry eyes 
• Loss of appetite or feeling sick 
• Skin rash, itchy skin 
• Diarrhoea  
• Joint pain 
• Headaches 
• Breathlessness and a dry cough 
• Changes in weight or body temperature (can be related to effects on the thyroid gland).

Some of the side effects, such as diarrhoea, can be serious. It is important to tell your doctor or nurse if you have any side effects with immunotherapy so that you can receive treatment as soon as possible.

Clinical trials 

Current clinical trials are studying the effectiveness of immunotherapy as a treatment for breast cancer. Talk to your medical oncologist about clinical trials that may be suitable for you. Read about clinical trials and breast cancer.