A cancer immunotherapy (anti-PD-1)
Cemiplimab
A cancer immunotherapy given as a drip that helps the immune system recognise and attack cancer cells.
What is Cemiplimab?
Cemiplimab (Libtayo) is a cancer immunotherapy given as a drip into a vein by an oncology team. It works by taking the 'brakes' off your immune system, blocking a protein called PD-1, so your own immune cells can find and attack cancer. Because it boosts the immune system, it can sometimes cause the immune system to attack healthy parts of the body — most often the bowel, liver, lungs, skin or hormone glands. These immune-related reactions can be serious and can appear during treatment or weeks to months afterwards, so report new symptoms promptly. You will have blood tests before each cycle and should carry an alert card.
Education and reference only. This is a plain-language guide to Cemiplimab — it deliberately contains no doses. Doses depend on the person, the brand and the reason for treatment, and belong with your prescriber. Always check the BNF, the product labelling (SmPC) and follow medical advice.
What it is
Cemiplimab is a type of cancer immunotherapy known as an immune checkpoint inhibitor. It is a man-made antibody that blocks a protein called PD-1 on immune cells, which some cancers use to hide from the immune system. It is used by oncology specialists to treat certain cancers, including some advanced skin cancers and others. It is given slowly into a vein as an infusion (a drip), usually as a course of repeated cycles in a hospital or chemotherapy day unit.
How it works
Cancer cells can switch off the immune system by pressing on a 'brake' called PD-1, which stops immune cells attacking them. Cemiplimab blocks this brake, freeing your immune cells (T-cells) to recognise the cancer as a threat and attack it. Because the same brakes normally protect your healthy tissues, releasing them can sometimes let the immune system attack healthy organs too — which is why immune-related side effects are the central thing to watch for with this whole group of medicines.
Company & origin
Originated / developed by: Regeneron / Sanofi.
A modern cancer immunotherapy given by specialist oncology teams in the UK as a drip, used for certain skin and other cancers.
Practical use
How to take Cemiplimab
General, dose-free guidance — always follow your prescriber's and the leaflet's specific instructions.
- It is given by your oncology team as a drip into a vein; you do not take it yourself at home.
- You will usually have it as repeated cycles, with blood tests before each one to check your organs and hormone levels.
- Report any new or worsening symptoms promptly — such as diarrhoea, breathlessness, cough, severe tiredness, yellowing skin or unusual thirst — even between appointments or after treatment ends.
- Carry the alert card you are given at all times, and show it to any doctor, nurse or pharmacist you see.
- Tell your team about all other medicines and conditions, and let them know before starting any steroids or new treatments elsewhere.
Weighing it up
Advantages & disadvantages of Cemiplimab
Advantages
- Can produce long-lasting responses in some cancers by harnessing the body's own immune system.
- Often better tolerated day to day than traditional chemotherapy, with no routine hair loss.
- Given as a planned drip in cycles, with close specialist monitoring throughout.
Disadvantages
- Can trigger immune-related side effects that affect healthy organs and may be serious.
- These reactions can appear weeks or months after treatment has stopped, so vigilance is needed for a long time.
- It does not work for everyone, and responses cannot be guaranteed.
Practical use
Good to know
The most important thing to understand is that cemiplimab can cause immune-related side effects, where the freed-up immune system attacks healthy organs. This can affect almost any part of the body: the bowel (diarrhoea or colitis), the liver (hepatitis), the lungs (pneumonitis, with cough or breathlessness), the skin (rash or itching) and the hormone glands such as the thyroid, pituitary and adrenal glands, and it can sometimes cause diabetes. These reactions can be serious and can begin during treatment or weeks to months after it finishes. The key message is to report new symptoms promptly — new or worsening diarrhoea, breathlessness, a new cough, severe tiredness, yellowing of the skin or eyes, or unusual thirst — because early treatment, often with steroids, works well and can prevent things becoming serious. You will have regular blood tests (including thyroid and liver checks) before each cycle, and you should carry the alert card you are given so any healthcare professional knows you are on immunotherapy.
Who should not take it / use with caution
- People with certain active autoimmune conditions may not be suitable, as immunotherapy can worsen them; your team will weigh this up carefully.
- Those who have had a serious immune reaction to this type of medicine before may be advised against further treatment.
- It is used with great caution, and only after specialist assessment, in people who have had an organ transplant.
Monitoring
- Blood tests before each cycle, including liver function and thyroid and other hormone checks.
- Regular reviews of any new symptoms that could signal an immune-related reaction.
- Scans to assess how the cancer is responding to treatment.
Side effects
- Immune-related effects can affect the bowel (diarrhoea, colitis), liver (hepatitis), lungs (pneumonitis with cough or breathlessness), skin (rash, itching) and hormone glands (thyroid, pituitary, adrenal, and sometimes diabetes).
- More general effects include tiredness, reduced appetite, nausea, joint or muscle aches and a reaction around the time of the drip.
- Rarely, serious reactions affecting the heart, nervous system, kidneys or eyes can occur and need urgent medical attention.
Key interactions
- Tell your team about all medicines, as long-term steroids or medicines that dampen the immune system may affect how it works.
- Other cancer treatments may be combined with it deliberately, but only under specialist guidance.
- Some herbal remedies and supplements that affect the immune system should be discussed with your team before use.
Available as: Given as an infusion (a drip) into a vein by an oncology team.
Answers
Cemiplimab: frequently asked questions
How does cemiplimab work?
It blocks a 'brake' called PD-1 on your immune cells, freeing them to recognise and attack cancer. Because the same brakes protect healthy tissue, it can sometimes cause immune-related side effects.
What symptoms should I report straight away?
Tell your team promptly about new or worsening diarrhoea, breathlessness, a new cough, severe tiredness, yellowing of the skin or eyes, or unusual thirst — early treatment, often with steroids, is important.
Can side effects happen after treatment has finished?
Yes. Immune-related reactions can appear weeks or even months after your last drip, so it is important to stay alert and report new symptoms even after treatment ends.
Why do I have so many blood tests?
Blood tests before each cycle check your liver, thyroid and other hormone glands so any immune-related effect can be caught and treated early.
Is it similar to pembrolizumab and nivolumab?
Yes. Like those medicines, cemiplimab blocks PD-1 to release the immune system's brakes against cancer, so it works in a very similar way and shares similar immune-related side effects.
Authoritative sources
- BNF
- NICE CKS
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