Immunotherapy for Breast Cancer: How It Works and Who It Helps

What is immunotherapy?

Immunotherapy is a type of cancer treatment that uses your body's own immune system to help find and destroy cancer cells. The immune system is your body's natural defence against illness. Cancer cells can sometimes hide from it or switch it off, so it does not attack them. Immunotherapy helps the immune system to recognise the cancer again.

According to Cancer Research UK, the main type of immunotherapy used for breast cancer is a group of drugs called checkpoint inhibitors. These are different from chemotherapy. Chemotherapy attacks the cancer cells directly, while immunotherapy works on the immune system so that it can do the attacking. The two are often given together.

Immunotherapy is a newer kind of breast cancer treatment. It is not suitable for everyone, and it is only used for certain types of breast cancer. This page explains how it works, who it may help and what to expect. It is general information, not personal medical advice. Your oncologist, breast care nurse and GP know your own situation, so please always check with your treatment team about what is right for you.

How do checkpoint inhibitors work?

Your immune system has natural 'brakes', called checkpoints, that stop it from attacking your healthy cells by mistake. These checkpoints are important and useful. The problem is that some cancers learn to press these brakes, which tells the immune system to leave the cancer alone.

Checkpoint inhibitor drugs work by releasing these brakes. The NHS explains that pembrolizumab works by blocking a specific protein on the surface of certain immune cells, which then seek out and destroy the cancer cells. In other words, the drug takes the 'off switch' away from the cancer, so the immune system is free to attack it.

One protein involved in this process is called PD-L1. Some breast cancers carry a lot of PD-L1, which can act as a shield against the immune system. For some treatments, your team may test the cancer for PD-L1 to help decide whether immunotherapy is likely to help you. Cancer Research UK notes that doctors may check for the PD-L1 protein on cancer cells when deciding on treatment for secondary triple-negative breast cancer.

The two checkpoint inhibitors used most often for breast cancer in the UK are pembrolizumab (brand name Keytruda) and atezolizumab (brand name Tecentriq). They are usually given together with chemotherapy rather than on their own, because the combination works better than either drug by itself.

Why immunotherapy is used mainly for triple-negative breast cancer

Not all breast cancers respond to immunotherapy. In the UK it is used mainly for triple-negative breast cancer. This is a type of breast cancer where the cells do not have receptors for the hormones oestrogen and progesterone, and do not make extra amounts of a protein called HER2. Because of this, treatments that target hormones or HER2 do not work for it.

Triple-negative breast cancer is less common than other types, but it tends to grow more quickly and is more often found in younger women. Because the usual targeted treatments do not work, finding new options has been a priority. Research has shown that triple-negative breast cancers often have more immune cells around them, which means they are more likely to respond to immunotherapy than some other breast cancer types.

This is why most immunotherapy for breast cancer is given for triple-negative disease. Research into using immunotherapy for other types of breast cancer is continuing, but for now its main role in routine NHS care is in triple-negative breast cancer.

It is worth remembering that triple-negative breast cancer can affect anyone, including younger women, and that outcomes are best when it is found early. Knowing the normal look and feel of your breasts, and reporting any new lump or change to your GP without delay, gives the widest range of treatment choices, including newer options like immunotherapy where they are suitable.

Who can have immunotherapy on the NHS?

Immunotherapy is available on the NHS for triple-negative breast cancer in two main situations. The exact rules are set by NICE (the National Institute for Health and Care Excellence), which decides which treatments the NHS should fund.

The first situation is early or locally advanced triple-negative breast cancer that has a high risk of coming back. According to NICE guidance (TA851), pembrolizumab is recommended for adults with this type of cancer. It is given with chemotherapy before surgery, to help shrink the tumour. This is called neoadjuvant treatment. It is then continued on its own after surgery, to lower the risk of the cancer returning. This is called adjuvant treatment.

The second situation is triple-negative breast cancer that has spread to another part of the body (secondary or metastatic breast cancer) or come back and cannot be removed by surgery. NICE has recommended both atezolizumab and pembrolizumab, each combined with chemotherapy, as options for some people in this situation whose cancer tests positive for the PD-L1 protein and who have not yet had chemotherapy for the spread cancer. PD-L1 testing helps the team work out who is likely to benefit.

Whether immunotherapy is right for you depends on the exact type and stage of your cancer, your PD-L1 result, your general health and other treatments you have had. Your oncologist will explain whether it is an option for you. NICE rules can change as new evidence appears, so your treatment team will always have the most up-to-date position for your situation.

How immunotherapy is given

Immunotherapy for breast cancer is usually given as a drip into a vein (an infusion). The NHS describes this as going in through a thin, short tube called a cannula that is placed into a vein in your arm or hand, or sometimes through a longer line that stays in place during your treatment.

Treatment is given in cycles, often every three to six weeks, in a chemotherapy day unit. A full course can last around a year, depending on your treatment plan. You can usually go home the same day. Your team will give you a clear schedule and a number to call if you feel unwell between visits.

In 2026, NHS England began rolling out a new injection (subcutaneous) form of pembrolizumab. NHS England says this version is given as a quick injection under the skin, taking around one to two minutes, instead of a drip that could last up to two hours. This can save a lot of time for patients and free up clinic capacity. NHS England reports that around 14,000 patients start pembrolizumab each year in England across many cancer types, and most are expected to be able to use the faster injection. Your team will tell you which form you will have.

Possible side effects

Because immunotherapy works by switching the immune system back on, it can sometimes make the immune system attack healthy parts of the body as well as the cancer. This can cause side effects in almost any organ. Most side effects are mild and can be managed, but some can be more serious, so it is important to report new symptoms early.

According to Cancer Research UK, common side effects of immunotherapy for breast cancer can include:

• Tiredness (fatigue) and loss of appetite.
• Low levels of blood cells, which can raise the risk of infection.
• Feeling or being sick (nausea or vomiting).
• Skin changes, such as red, sore or itchy skin, or a rash.
• Flu-like symptoms, such as chills, fever and dizziness.
• Diarrhoea (loose or watery poo).

Less often, immunotherapy can cause inflammation in organs such as the bowel, lungs, liver, or hormone glands like the thyroid. The NHS explains that, in rare cases, side effects can be serious or even life-threatening, which is why your team will watch you closely and may do regular blood tests.

Tell your treatment team straight away if you have severe or lasting diarrhoea, breathlessness or a new cough, severe tummy pain, yellowing of your skin or eyes, a bad skin rash, or feel very unwell. Acting quickly means side effects can usually be treated, often with steroids to calm the immune system down. Always use the emergency contact number your team gives you, day or night, rather than waiting.

The current UK and NICE position

Immunotherapy is now an established part of NHS treatment for triple-negative breast cancer in the UK, but only for the specific groups described above. It is not used routinely for hormone-positive or HER2-positive breast cancer outside of clinical trials.

NICE reviews the evidence and decides which treatments the NHS funds, and it updates its guidance as new research appears. Cancer Research UK and the NHS both note that immunotherapy is an active area of research, with trials looking at new drugs and at using immunotherapy for more types of breast cancer. If you are interested, you can ask your oncologist whether any clinical trials might be suitable for you.

Wider access to new treatments depends first on people being diagnosed early, when more options are available. This is at the heart of our charity's mission: supporting earlier detection and fairer access to good care in underserved communities, so that no one misses out on the treatments that could help them. If you notice any new breast changes, the NHS advises seeing your GP without delay.