Pembrolizumab (Keytruda)

Pembrolizumab is a targeted therapy. It’s also referred to as an immunotherapy.

Immunotherapy cancer treatments use the body’s natural defence system (immune system) to help them fight cancer.

Pembrolizumab is the drug’s non-branded name. You may hear it called by its brand name Keytruda.

Pembrolizumab can be given on its own and with chemotherapy.

You may be offered pembrolizumab if you have triple negative breast cancer.

Primary breast cancer

You may be offered pembrolizumab if your triple negative breast cancer has a higher risk of returning (recurrence).

Locally advanced or metastatic (secondary) breast cancer

You may be offered pembrolizumab if you have triple negative locally advanced breast cancer or metastatic breast cancer:

• That has a higher-than-normal level of a protein called PDL1
• Which has not previously been treated with chemotherapy

You may be tested first to see if you would benefit from another similar drug called atezolizumab. The tests measure levels of the protein PDL1 using tissue removed during a biopsy or surgery.

You may also be offered pembrolizumab as part of a clinical trial.

Your immune system usually protects you from infection and illness. It does this by recognising and attacking unfamiliar substances and germs like viruses and bacteria, and abnormal cells like cancer cells. Sometimes the body’s natural immune system is not able to do this. 

PDL1 is a protein that usually stops your immune system attacking healthy cells in the body.

Some breast cancer cells have a higher-than-normal level of PDL1. This allows them to trick your immune system and avoid being attacked as abnormal cells. They can then continue to grow.

Pembrolizumab blocks the PDL1 protein, helping your immune system find and destroy breast cancer cells.

Breast cancer that has a higher-than-normal level of PDL1 is called PDL1-positive.

Pembrolizumab is given as a drip into a vein (intravenously) over 30 minutes.

The drug may be given through a tube put into your vein (cannula) each time you have treatment. It can also be given through a device that stays in place throughout the course of treatment, such as a central line or port.

Find out more about the different ways chemotherapy can be given.

You’ll be asked to stay in the hospital for a few hours after your first treatment to make sure you feel well.

Pembrolizumab can also be given as an injection into the fatty tissue under the skin (subcutaneous injection) but isn’t currently widely used in breast cancer. Your treatment team will let you know how your treatment will be given.

To treat primary breast cancer

Before surgery

Pembrolizumab is usually given every 3 weeks for 8 cycles, in combination with chemotherapy.

However, you may have pembrolizumab every 6 weeks. If this is the case, you'll still have chemotherapy every 3 weeks.

Your treatment team will tell you which chemotherapy drugs you will be given.

After surgery

After surgery, you’ll have pembrolizumab on its own every 3 or 6 weeks for up to 9 cycles.

Your treatment team will tell you whether you'll have pembrolizumab every 3 or 6 weeks.

To treat locally advanced or metastatic breast cancer

You’ll have pembrolizumab with either paclitaxel or nab-paclitaxel (Abraxane). Nab-paclitaxel is a combination of paclitaxel and albumin.

You’ll either have pembrolizumab every 3 weeks or every 6 weeks, depending on the dose you’re prescribed.

You’ll be given pembrolizumab with chemotherapy:

• For as long as your treatment team feels you’re benefitting from these drugs and any side effects are manageable
• For up to 2 years (or after 35 treatments every 3 weeks, or its equivalent if it’s given every 6 weeks)

Like any drugs, pembrolizumab and chemotherapy can cause side effects. It’s sometimes difficult to know which side effects are being caused by which treatment.

Side effects from pembrolizumab can occur in any part of the body at any time during treatment. They can also sometimes occur months after treatment has finished.

Everyone reacts differently to drugs and some people have more side effects than others. Many side effects can be controlled and those described here will not affect everyone.

This information does not list all the possible side effects of pembrolizumab and chemotherapy. If you’re concerned about any side effects, regardless of whether they’re listed here or on the alert card, contact your treatment team.

Effects of pembrolizumab on your immune system

Pembrolizumab may cause immune-related side effects. This is when healthy cells get destroyed by the body's immune system and cause inflammation of the tissues and organs.

Symptoms can vary depending on where in the body the inflammation is. They can appear at any time during or after treatment.

Reporting symptoms to your treatment team and getting medical treatment quickly is important to help prevent the side effects worsening. Your alert card will also list these symptoms to report immediately.

Lung inflammation

• A new or worsening cough
• Shortness of breath
• Chest pain

Bowel inflammation

• Diarrhoea that doesn’t go away
• Blood or mucus in your poo
• Dark coloured poo
• Abdominal pain

Liver inflammation

• Yellowing of the skin or whites of the eyes
• Feeling sick (nausea) and being sick (vomiting)
• Bleeding and bruising more easily than normal
• Dark coloured pee
• Pain in the upper tummy

Inflammation of the hormone glands

• Extreme tiredness (fatigue)
• Headache that doesn’t go away
• Changes to your weight
• Changes to your mood
• Changes to your bowel habits, like diarrhoea or constipation
• Dizziness or fainting
• Feeling more hungry or thirsty than usual
• Peeing more often than usual
• Increased sensitivity to heat or cold

Heart inflammation

• Chest pain
• Shortness of breath
• Irregular heartbeat
• Not being able to exercise for as long as normal
• Swelling of the ankles

Brain inflammation

• Neck stiffness
• Headache
• Fever
• Chills
• Being sick (vomiting)
• Eye sensitivity to light
• Confusion
• Difficulty sleeping

Nerve inflammation

• Muscle weakness
• Changed sensation, such as numbness or pins and needles in the arms and legs
• Dizziness

Pancreas inflammation

• Tummy pain
• Feeling sick (nausea) and being sick (vomiting)

Eye inflammation

• Eye pain
• Changes to your vision
• Itchiness or redness
• Sensitivity to light

Muscle inflammation

• Muscle aches

Kidney inflammation

• Peeing more or less often than usual
• Changes to the colour of your pee
• Swelling anywhere in the body
• Pain in the lower tummy (pelvis)

Common side effects

Effects on the blood

Treatment with pembrolizumab and chemotherapy can temporarily affect the number of blood cells in the body. Blood is made up of red cells, white cells and platelets.

You’ll have regular blood tests. If these show the number of blood cells is too low, your next cycle of treatment may be delayed or the dose of chemotherapy reduced. 

If your blood tests show possible inflammation in your kidneys or liver, your treatment will be delayed and you may need steroids.

Risk of infection

Not having enough white blood cells can increase the risk of getting an infection.

Before starting pembrolizumab, you should be given an alert card with a contact number or told who to contact if you feel unwell at any time during your treatment, including overnight or at the weekends.  

You may need treatment if you get an infection.  

Sometimes your treatment team may recommend injections of drugs called growth factors. This helps the body make more white blood cells to reduce your risk of infection.

Anaemia

Having too few red blood cells is called anaemia. If you feel particularly tired, out of breath or dizzy, let your treatment team know.

Bruising and bleeding

Pembrolizumab can reduce the number of platelets. Platelets help the blood to clot.

If your platelets are low, you may:

• Bruise more easily 

• Have nosebleeds 

• Notice that your gums bleed when you brush your teeth 

• Take longer to stop bleeding if you cut yourself 

Tell your treatment team if you have any of these symptoms.

Nausea and vomiting

You may feel sick (nausea) and be sick (vomit).

You’ll be given anti-sickness medication before you have chemotherapy. You’ll also be given anti-sickness tablets to take at home.

If you continue to feel sick or vomit, tell your treatment team as they may be able to change your anti-sickness drugs.

Loss of appetite

You may not feel like eating, especially if you feel sick.

It might help to eat small meals regularly and drink plenty of liquids. You can also ask your treatment team to refer you to a dietitian for more advice.

Find out more about diet and breast cancer.

Constipation and diarrhoea

Pembrolizumab and chemotherapy may affect your digestive system in different ways. Some people get constipated, while others have diarrhoea.

Let your treatment team know if you have either of these. They can prescribe medication to help.

Contact your chemotherapy team if you have diarrhoea 3 or more times in 24 hours, compared to what’s usual for you.

Extreme tiredness (cancer-related fatigue)

Fatigue is extreme tiredness that does not go away with rest or sleep.

It’s one of the most common symptoms in people with metastatic breast cancer.

Fatigue may affect how you cope with your cancer and its treatment. It can also make everyday activities harder and affect your quality of life.

If you think you have fatigue, tell your GP or treatment team. They can assess you and offer advice on how to manage your energy levels. 

Find out more about managing fatigue.

Painful muscles and joints

Your muscles or joints may ache or become painful after you’ve had your treatment. This is often mild and temporary, but for some people it’s severe and longer lasting.

It can usually be relieved with mild pain relief like paracetamol or an anti-inflammatory drug such as ibuprofen. Before using anti-inflammatory pain relief, ask your treatment team about the correct dose, how long you should use it for and any possible side effects, especially if you have a stomach ulcer or asthma.

Exercise that gently stretches your joints or strengthens your muscles to better support your joints, such as yoga or Pilates, may help improve your symptoms. Brisk walking can also be beneficial. A physiotherapist may also be able to suggest exercises to help. If you have metastatic breast cancer, check with your treatment team before starting any new type of exercise.

Skin reactions

You may develop a rash on your body, or your skin might look a different colour (discoloured). This could be red or darkened and itchy, or you may feel flushed.

If you have a skin reaction, tell your treatment team so they can monitor your symptoms. They may be able to prescribe medicine to help.

Contact your treatment team if the rash covers a large area of your body.

Nail changes

After a few cycles of chemotherapy, the colour of your nails may change. They could also become brittle, crack or change in texture, for example ridges may form. Some people lose nails on their fingers or toes during treatment, but they usually grow back.

Hair loss

Pembrolizumab can cause hair thinning and hair loss.

Numbness and tingling in hands or feet

You may have numbness or tingling in your hands or feet. This is due to the effect pembrolizumab and chemotherapy can have on the nerves and is known as peripheral neuropathy.

In most cases it’s mild and goes away soon after treatment stops, although in some cases it can be permanent. If it’s severe, your treatment team may reduce the dose of chemotherapy or stop it completely.

If you have numbness or tingling, tell your treatment team so they can monitor your symptoms.

Less common side effects

Sore mouth

Your mouth may become sore and small ulcers may develop.

Looking after your mouth, including your teeth and gums, is very important during treatment.

You’ll usually be given mouthwash to try to reduce soreness and prevent mouth ulcers developing. It’s a good idea to use a small, soft toothbrush during this time.  

See your dentist for a check-up before treatment with pembrolizumab and chemotherapy begins. Avoid dental work during treatment if possible.

If you do need to have dental work during treatment, talk with your treatment team about the best time to have this.

If you’re having difficulty registering with a dentist, let your treatment team know.  

Taste changes

Your taste may change and some foods may taste different, for example more salty, bitter or metallic. 

Our information on diet during breast cancer treatment includes tips for dealing with taste changes.

Blood clots

People with breast cancer have a higher risk of blood clots. Having pembrolizumab with chemotherapy also increases the risk of blood clots such as a DVT (deep vein thrombosis).

If you have a DVT, there’s a risk part of the blood clot could break away and travel to the lung. This is known as a pulmonary embolism (PE).

Blood clots can be life-threatening and should be treated quickly.

Taking other medications

It’s important to tell your treatment team about any prescribed or over-the-counter medicines you’re taking. This includes any herbal medicines or supplements, steroids or drugs that affect the body’s immune system.

Sex, contraception and pregnancy

You can still have sex during treatment. It’s thought some drugs used to treat breast cancer cannot pass into vaginal fluids or semen, but this cannot be completely ruled out.

Most treatment teams will advise using barrier methods of contraception, such as condoms or female condoms, during treatment and for a few days after chemotherapy is given. 

You’re advised not to become pregnant while having treatment because pembrolizumab and chemotherapy may harm a developing baby. If you have not been through the menopause, talk to your treatment team about the most suitable method of contraception for you. It’s still possible to become pregnant even if your periods are irregular or have stopped naturally or because of treatment for breast cancer.

Find out more about how breast cancer and its treatment can affect sex and intimacy and read our tips on how to manage these changes.

Fertility

It’s not known whether pembrolizumab affects fertility. You can talk to your treatment team about possible fertility preservation options before starting treatment.

Breastfeeding

Breastfeeding is not recommended while having pembrolizumab and chemotherapy. This is because there’s a risk the drugs could be passed on through breast milk.

Travel and vaccinations

If you’re planning a holiday or need to travel overseas, check with your treatment team first.  

You should not have any live vaccines while you’re having treatment. 

For more information about vaccines, including COVID-19 and flu vaccines, see our information on vaccines and breast cancer.

You can call our helpline, below, to speak to one of our specialist nurses if you’ve got any questions or worries.

You can also join our online forum to speak to others who are having similar treatment to you.

Primary breast cancer 

Being diagnosed with primary breast cancer can make you feel lonely and isolated. But there’s support available. And you might find it helpful to talk to someone who knows what it’s like.

Our Someone Like Me service can match you with a trained volunteer who’s had a similar experience to you. They'll be a phone call or email away to answer your questions, offer support or simply listen. Because there’s nothing like finding someone who really understands.

Metastatic breast cancer 

If you’ve been diagnosed with metastatic breast cancer, you might be feeling lonely or isolated.

Some people find it helps to talk to someone who has been through the same experience as them. You might find it helpful to visit our confidential online forum.

Our Living with Secondary Breast Cancer services are also here for you. Choose the type of support that suits you and you’ll be able to talk, listen and learn with people who understand the challenges that metastatic breast cancer can bring. Find out more below.