Immunotherapy for Merkel Cell Carcinoma

Immunotherapy is the use of medicines that help a person’s own immune system find and destroy cancer cells. This is a promising newer form of treatment for Merkel cell carcinoma (MCC), especially if the cancer has spread to other parts of the body.

Immune checkpoint inhibitors

An important part of the immune system is its ability to keep itself from attacking normal cells in the body. To do this, it uses “checkpoints” – proteins on immune cells that need to be turned on (or off) to start an immune response. Cancer cells sometimes use these checkpoints to avoid being attacked by the immune system. 

For example, PD-1 is a checkpoint protein on immune cells called T cells. It normally acts as a type of “on/off switch” that can help keep the T cells from attacking other cells in the body. It switches “off” when it attaches to PD-L1, a protein on some normal (and cancer) cells. This basically tells the T cell to leave the other cell alone. Some cancer cells have large amounts of PD-L1, which helps them evade immune attack. 

Drugs that block either PD-1 or PD-L1 can stop this binding and boost the immune response against cancer cells. Examples of such drugs include:

  • Avelumab (Bavencio), which targets PD-L1
  • Pembrolizumab (Keytruda), which blocks PD-1

These drugs are given as an intravenous (IV) infusion, typically every 2 or 3 weeks. They have been shown to shrink or slow the growth of some advanced MCC tumors, sometimes even after other treatments have been tried. 

Some other immune checkpoint inhibitors are now being studied for use against MCC as well.

Possible side effects

Side effects of these types of drugs can include: 

  • Fatigue
  • Cough
  • Nausea
  • Rash or itchy skin
  • Joint pain
  • Loss of appetite
  • Diarrhea
  • Constipation

Other, more serious side effects occur less often: 

Infusion reactions: Some people might have an infusion reaction while getting one of these drugs. This is like an allergic reaction, and can include fever, chills, flushing of the face, rash, itchy skin, wheezing, and trouble breathing. You might be given medicines before each infusion to help lower the risk of this happening.

Autoimmune reactions: These drugs work by basically removing the brakes on the body’s immune system. Sometimes the immune system starts attacking other parts of the body, which can cause serious or even life-threatening problems in the lungs, intestines, liver, hormone-making glands, kidneys, or other organs.

It’s very important to report any new side effects to your health care team right away. If serious side effects do occur, treatment may need to be stopped and you may get high doses of corticosteroids to suppress your immune system.


The American Cancer Society medical and editorial content team
Our team is made up of doctors and master's-prepared nurses with deep knowledge of cancer care as well as journalists, editors, and translators with extensive experience in medical writing.

Last Medical Review: March 27, 2017 Last Revised: March 27, 2017

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