Cemiplimab

Say it: seh-MIP-lih-mab · Brand names: Libtayo

Cemiplimab is an immunotherapy medicine that helps your own immune system fight cancer.

What it is

Cancer cells can hide from the immune system by pressing a brake called PD-1 on immune cells. Cemiplimab blocks this brake. This helps your immune system find and attack the cancer.

Often used for

• squamous cell skin cancer
• basal cell skin cancer
• non-small cell lung cancer

How you get it

Cemiplimab is given through a vein (IV) in a clinic. The infusion takes about 30 minutes. It is usually given once every 3 weeks. Your schedule may be different.

Common side effects and what helps

• Feeling tired. Rest and short walks can help.
• Rash or itchy skin. Use gentle soap and unscented lotion, and tell your team.
• Diarrhea. Drink plenty of fluids and tell your team, because it can be a sign of bowel inflammation.
• Muscle or joint aches. Ask your team which pain medicine is safe.
• Not feeling hungry. Eat small snacks during the day.
• Upset stomach. Eat small meals and drink fluids slowly.

Call your care team right away if you have

• Diarrhea, belly pain, or bloody or black stools
• A new or worse cough, chest pain, or shortness of breath
• Yellow skin or eyes, very dark pee, or pain on the right side of the belly
• Bad headache, extreme tiredness, dizziness, or feeling very cold or very hot
• Feeling very thirsty, peeing a lot, or confusion (signs of high blood sugar)
• Chest pain, a fast or uneven heartbeat, or muscle weakness
• A rash with blisters, peeling skin, or sores in the mouth

Before you start, tell your team

• If you have an autoimmune disease, such as Crohn's disease, ulcerative colitis, lupus, or rheumatoid arthritis
• If you have had an organ transplant or a stem cell transplant, or plan to have one
• If you have lung or breathing problems, or have had radiation to the chest
• If you have a nerve or muscle disease, such as myasthenia gravis or Guillain-Barre syndrome
• If you are pregnant, may become pregnant, or are breastfeeding
• All the medicines, vitamins, and herbal products you take, including steroids

Good to know

• It can make the immune system attack healthy organs, such as the lungs, bowel, liver, glands, kidneys, or skin. This can happen during treatment or months after it ends.
• You will have blood tests to check your liver, kidneys, thyroid, and blood sugar.
• If a side effect happens, your team may pause treatment and give you steroids. Tell every doctor you see that you are on immunotherapy.
• Some people have a reaction during the infusion, such as chills, flushing, or trouble breathing. Your nurse will watch you.
• It can harm an unborn baby. Use birth control during treatment and for a while after, as your team tells you.

Questions to ask

• How often will I get this medicine, and for how long?
• Which side effects mean I should call right away?
• Who do I call at night or on weekends?
• How will we know if it is working?

Side effect guides

• Fatigue (tiredness)
• Diarrhea
• Skin rash (including EGFR-inhibitor rash)
• Pain
• Immunotherapy side effects

Last updated: 2026-10-27. Medically reviewed by Veli Bakalov, MD, medical oncologist (October 2026). General education from Step by Step, the patient portal of HemeOncBuddy.