Cemiplimab (Libtayo)

Cemiplimab is a monoclonal antibody Open a glossary item. Some monoclonal antibodies are a type of immunotherapy Open a glossary item.

Cemiplimab stimulates the immune system Open a glossary item to attack cancer cells. It is also known as Libtayo.

It is a treatment for advanced cutaneous squamous cell carcinoma (SCC). 

You pronounce cemiplimab as seh-mip-lih-mab.

How does cemiplimab work?

Cemiplimab is an immunotherapy called a checkpoint inhibitor Open a glossary item. It stimulates the body’s immune system to attack cancer cells.

Cemiplimab targets and blocks a protein called PD-1 on the surface of certain immune cells called T cells. Blocking PD-1 triggers the T cells to find and kill cancer cells.

How do you have cemiplimab?

You have cemiplimab as a drip into your bloodstream.

You might have treatment through a long plastic tube that goes into a large vein in your chest. The tube stays in place throughout the course of treatment. This can be a:

  • central line
  • PICC line
  • portacath

If you don't have a central line

You might have treatment through a thin short tube (a cannula) that goes into a vein in your arm. You have a new cannula each time you have treatment.

How often do you have cemiplimab?

You have cemiplimab as cycles of treatment. This means that you have the drug and then a rest to allow your body to recover.

You have cemiplimab as a drip (infusion) over about 30 minutes. You have it once every 3 weeks.

You may have cemiplimab for up to 2 years as long as it is working and the side effects aren't too bad.


You have blood tests before and during your treatment. They check your levels of blood cells and other substances in the blood. They also check how well your liver and kidneys are working.

What are the side effects of cemiplimab?

Side effects can vary from person to person. They also depend on what other treatment you are having. 

This treatment affects the immune system. This may cause inflammation in different parts of the body which can cause serious side effects. They could happen during treatment, or some months after treatment has finished. In some people, these side effects could be life threatening.

When to contact your team

Your doctor, pharmacist or nurse will go through the possible side effects. They will monitor you closely during treatment and check how you are at your appointments. Contact your advice line as soon as possible if:

  • you have severe side effects

  • your side effects aren’t getting any better

  • your side effects are getting worse

Early treatment can help manage side effects better. 

Contact your healthcare team immediately if you have signs of infection, including a temperature above 37.5C or below 36C.

We haven't listed all the side effects here. Remember it is very unlikely that you will have all of these side effects, but you might have some of them at the same time.

Common side effects

These side effects happen in more than 10 in 100 people (more than 10%). You might have one or more of them. They include:

Lung problems 

You might develop a cough or breathing problems. This could be due to infection, such as pneumonia or inflammation of the lungs (pneumonitis). 

Let your doctor or nurse know straight away if you suddenly become breathless or develop a cough.

You may also develop infection in the tonsils or throat or have pain in the sinuses. Tell your doctor straight away if you experience any signs of infection.

Breathlessness and looking pale

You might be breathless and look pale due to a drop in red blood cells. This is called anaemia.

Loss of appetite

You might lose your appetite for various reasons while having cancer treatment. Sickness, taste changes or tiredness can put you off food and drinks.

Diarrhoea or constipation 

Tell your healthcare team if you have diarrhoea or constipation. They can give you medicine to help. 

It is very important that you contact your healthcare team if you get diarrhoea as this could be a sign of colitis, a more serious complication.

Feeling or being sick

Feeling or being sick is usually well controlled with anti sickness medicines. It might help to avoid fatty or fried foods, eat small meals and snacks and take regular sips of water. Relaxation techniques might also help.

It is important to take anti sickness medicines as prescribed even if you don’t feel sick. It is easier to prevent sickness rather than treat it once it has started.

Tummy (abdominal) pain

Tell your treatment team if you have this. They can check the cause and give you medicine to help. 

Skin problems 

You might develop a rash or itchy skin

Occasionally you may develop patches of thick, scaly or crusty skin. Let your doctor know about any unusual skin problems. 

Tiredness and weakness (fatigue)

Tiredness and weakness (fatigue) can happen during and after treatment. Doing gentle exercises each day can keep your energy up. Don't push yourself, rest when you start to feel tired and ask others for help.

Joint or muscle pain

You might feel some pain from your muscles and joints. Speak to your doctor or nurse about what painkillers you can take to help with this.

Occasional side effects

These side effects happen in between 1 and 10 out of every 100 people (between 1 and 10%). You might have one or more of them. They include:

  • urinary tract infection - including stinging, burning or pain when you pass urine
  • an allergic reaction that can cause a rash, shortness of breath, redness or swelling of the face and dizziness
  • lower levels of hormone made by your thyroid gland – you might feel tired, cold, sad or depressed
  • higher levels of hormones made by your thyroid gland which can cause irregular or fast heart rate (palpitations), weight loss, anxiety and mood swings
  • headache
  • high blood pressure
  • numbness and tingling in fingers and toes (peripheral neuropathy)
  • black or tarry poo (stools)
  • changes to the way your liver and kidneys work – regular blood tests will check for this
  • sore mouth
  • swelling (oedema) in parts of the body such as hands, feet, face
  • a temperature (fever)
  • inflammation of the bowel (colitis) symptoms can include diarrhoea, passing blood when you have a poo, urgency to have a poo, and tummy pain
  • liver problems
  • tingling sensation in your arms or legs (nerve pain)

Rare side effects

These side effects happen in fewer than 1 in 100 people (less than 1%). You might have one or more of them. They include:

  • bruising or bleeding due to low platelets
  • heart problems including swelling of the lining of the heart and heart muscle, shortness of breath and chest pain
  • dryness in parts of the body including the eyes, mouth, nose, throat and skin (Sjogren’s syndrome)
  • weak, painful aching muscles
  • stiffness in the hips, neck and shoulders (polymyalgia rheumatica)
  • low levels of hormones from the adrenal gland – causing weakness, tiredness, and loss of appetite

Other side effects

Cemiplimab can cause your immune system Open a glossary item to treat an organ transplant Open a glossary item like a foreign body. This means your body could reject the organ. There isn't enough information to work out how often this side effect might happen. Contact your healthcare team if you feel unwell.

Coping with side effects

We have more information about side effects and tips on how to cope with them.

What else do you need to know?

Other medicines, food and drink 

Cancer drugs can interact with medicines, herbal products, and some food and drinks. We are unable to list all the possible interactions that may happen. An example is grapefruit or grapefruit juice which can increase the side effects of certain drugs.

Tell your healthcare team about any medicines you are taking. This includes vitamins, herbal supplements and over the counter remedies. Also let them know about any other medical conditions or allergies you may have.


It is not known whether this treatment affects fertility Open a glossary item in people. Talk to your doctor before starting treatment if you think you may want to have a baby in the future.

Contraception and pregnancy 

This drug may harm a baby developing in the womb. It is important not to become pregnant or get someone pregnant while you are having treatment with this drug and for at least 4 months afterwards.

Talk to your doctor or nurse about effective contraception before starting treatment. Let them know straight away if you or your partner become pregnant while having treatment.


Don’t breastfeed during this treatment because the drug may come through into your breast milk. Do not breastfeed for at least 4 months after the last dose.

Treatment for other conditions 

If you are having tests or treatment for anything else, always mention your cancer treatment. For example, if you are visiting your dentist.


Don’t have immunisations with live vaccines while you’re having treatment and for up to 12 months afterwards. The length of time depends on the treatment you are having. Ask your doctor or pharmacist how long you should avoid live vaccinations.

In the UK, live vaccines include rubella, mumps, measles, BCG, yellow fever and one of the shingles vaccines called Zostavax.

You can have:

  • other vaccines, but they might not give you as much protection as usual
  • the flu vaccine (as an injection)
  • the coronavirus (COVID-19) vaccine - talk to your doctor or pharmacist about the best time to have it in relation to your cancer treatment

Members of your household who are aged 5 years or over are also able to have the COVID-19 vaccine. This is to help lower your risk of getting COVID-19 while having cancer treatment and until your immune system Open a glossary item recovers from treatment.

Contact with others who have had immunisations - You can be in contact with other people who have had live vaccines as injections. Avoid close contact with people who have recently had live vaccines taken by mouth (oral vaccines) such as the oral typhoid vaccine. Sometimes people who have had the live shingles vaccine can get a shingles type rash. If this happens they should keep the area covered.

If your immune system is severely weakened, you should avoid contact with children who have had the flu vaccine as a nasal spray as this is a live vaccine. This is for 2 weeks following their vaccination.

Babies have the live rotavirus vaccine. The virus is in the baby’s poo for about 2 weeks and could make you ill if your immunity is low. Get someone else to change their nappies during this time if you can. If this isn't possible, wash your hands well after changing their nappy.

More information about this treatment

For further information about this treatment and possible side effects go to the electronic Medicines Compendium (eMC) website. You can find the patient information leaflet on this website.

You can report any side effect you have to the Medicines Health and Regulatory Authority (MHRA) as part of their Yellow Card Scheme.

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