Skip to main content


Pronunciation: ZYE-niz

Generic name: retifanlimab-dlwr
Dosage form: injection

Medically reviewed by Judith Stewart, BPharm. Last updated on Mar 23, 2023.

What is Zynyz?

Zynyz is a prescription medicine used to treat a type of skin cancer called Merkel cell carcinoma in adults.

Zynyz is a programmed death receptor-1 (PD-1)–blocking antibody (also called an immune checkpoint inhibitor) that works by binding to the PD-1 protein on immune T-cells to prevent the interaction with PD-L1, a protein that is often found on some cancer cells.

When the PD-1 protein on an immune cell interacts with the PD-L1 protein on a cancer cell, the cancer cell is considered healthy and is left alone. By blocking the interaction with PD-1, Zynyz works to remove the "brakes" on the immune system, allowing it to attack cancer cells more effectively.

What is Zynyz used to treat?

Zynyz is used for the treatment of adult patients with a type of skin cancer called Merkel cell carcinoma that is metastatic (cancer has spread to other parts of the body) or is recurrent locally advanced (cancer has returned).

Merkel cell carcinoma (MCC) is a rare and aggressive type of skin cancer that usually appears as a painless, reddish-purple skin nodule on the head, neck and arms in skin exposed to the sun. MCC tends to be a fast growing cancer with a high rate of metastatic disease which means it can spread quickly to other parts of the body. 

Zynyz was approved for Merkel cell carcinoma under the accelerated approval program by the U.S. FDA based on tumor response rate and duration of response (DOR). Continued approval may require further clinical trials to confirm clinical benefit.

It is not known if this medicine is safe and effective in children.

Important information

Zynyz is a medicine that may treat Merkel cell carcinoma by working with your immune system. It can cause your immune system to attack normal organs and tissues in any area of your body and can affect the way they work. These problems can sometimes become severe or life-threatening and can lead to death. You can have more than one of these problems at the same time. These problems may happen anytime during treatment or even after your treatment has ended.

Call or see your healthcare provider right away if you develop any new or worsening signs or symptoms, including:

Lung problems.

  • cough
  • shortness of breath
  • chest pain

Intestinal problems.

  • diarrhea (loose stools) or more frequent bowel movements than usual
  • stools that are black, tarry, sticky, or have blood or mucus
  • severe stomach-area (abdomen) pain or tenderness

Liver problems.

  • yellowing of your skin or the whites of your eyes
  • severe nausea or vomiting
  • pain on the right side of your stomach area (abdomen)
  • dark urine (tea colored)
  • bleeding or bruising more easily than normal

Hormone gland problems.

  • headaches that will not go away or unusual headaches
  • eye sensitivity to light
  • eye problems
  • rapid heartbeat
  • increased sweating
  • extreme tiredness
  • weight gain or weight loss
  • feeling more hungry or thirsty than usual
  • urinating more often than usual
  • hair loss
  • feeling cold
  • constipation
  • your voice gets deeper
  • dizziness or fainting
  • changes in mood or behavior, such as decreased sex drive, irritability, or forgetfulness

Kidney problems.

  • decrease in your amount of urine
  • blood in your urine
  • swelling of your ankles
  • loss of appetite

Skin problems.

  • rash
  • itching
  • skin blistering or peeling
  • painful sores or ulcers in your mouth or nose, throat, or genital area
  • fever or flu-like symptoms
  • swollen lymph nodes

Problems can also happen in other organs and tissues. These are not all of the signs and symptoms of immune system problems that can happen during treatment with this medicine. Call or see your healthcare provider right away for any new or worsening signs or symptoms, which may include:

  • chest pain, irregular heartbeat, shortness of breath, or swelling of ankles
  • confusion, sleepiness, memory problems, changes in mood or behavior, stiff neck, balance problems, tingling or numbness of the arms or legs
  • double vision, blurry vision, sensitivity to light, eye pain, changes in eyesight
  • persistent or severe muscle pain or weakness, muscle cramps
  • low red blood cells, bruising

Infusion reactions that can sometimes be severe. Signs and symptoms of infusion reactions may include:

  • chills or shaking
  • itching or rash
  • flushing
  • shortness of breath or wheezing
  • dizziness
  • feel like passing out
  • fever
  • back or neck pain

Rejection of a transplanted organ. Your healthcare provider should tell you what signs and symptoms you should report and monitor you, depending on the type of organ transplant that you have had.

Complications, including graft-versus-host disease, in people who have received a bone marrow (stem cell) transplant that uses donor stem cells (allogeneic). These complications can be serious and can lead to death. These complications may happen if you underwent transplantation either before or after being treated with Zynyz. Your healthcare provider will monitor you for these complications.

Getting medical treatment right away may help keep these problems from becoming more serious.
Your healthcare provider will check you for these problems during your treatment. Your healthcare provider may treat you with corticosteroid or hormone replacement medicines. Your healthcare provider may also need to delay or completely stop treatment if you have severe side effects.

Before you receive Zynyz

Before you start treatment, tell your healthcare provider about all of your medical conditions, including if you:

  • have immune system problems such as Crohn’s disease, ulcerative colitis, or lupus
  • have received an organ transplant
  • have received or plan to receive a stem cell transplant that uses donor stem cells (allogeneic)
  • have received radiation treatment to your chest area
  • have a condition that affects your nervous system, such as myasthenia gravis or Guillain-Barré syndrome


Tell your healthcare provider if you are pregnant or plan to become pregnant. Zynyz can harm your unborn baby.

Females who are able to become pregnant:

  • Your healthcare provider should do a pregnancy test before you start treatment.
  • You should use an effective method of birth control during your treatment, and for 4 months after your last dose. Talk to your healthcare provider about birth control methods that you can use during this time.
  • Tell your healthcare provider right away if you become pregnant or think you may be pregnant during treatment.


Tell your healthcare provider if you are breastfeeding or plan to breastfeed. It is not known if Zynyz passes into your breast milk.

Do not breastfeed during treatment, and for 4 months after your last dose.

What other drugs will affect Zynyz?

Tell your healthcare provider about all the medicines you take, including prescription and over-the-counter medicines, vitamins, and herbal supplements.

How will I receive Zynyz?

Your healthcare provider will give you Zynyz into your vein through an intravenous (IV) line over 30 minutes.

Zynyz is usually given every 4 weeks. Your healthcare provider will decide how many treatments you will need.

Your healthcare provider will do blood tests to check you for side effects.

If you miss any appointments, call your healthcare provider as soon as possible to reschedule your appointment.

Dosing information

Usual Adult Dose for Merkel Cell Carcinoma

500 mg as an intravenous infusion over 30 minutes every 4 weeks until disease progression, unacceptable toxicity, or up to 24 months.

Use: For the treatment of adult patients with metastatic or recurrent locally advanced Merkel cell carcinoma.

Zynyz side effects

Zynyz can cause serious side effects. See Important information.

The most common side effects include:

  • tiredness
  • muscle and bone pain
  • itching
  • diarrhea
  • rash
  • fever
  • nausea

These are not all the possible side effects. Call your doctor for medical advice about side effects. You may report side effects to FDA at 1-800-FDA-1088.

General information about the safe and effective use of Zynyz

Medicines are sometimes prescribed for purposes other than those listed in a Medication Guide. If you would like more information, talk with your healthcare provider. You can ask your healthcare provider for information that is written for health professionals.

What are the ingredients in Zynyz?

Active ingredient: retifanlimab-dlwr
Inactive ingredients: glacial acetic acid, polysorbate 80, sodium acetate, sucrose, and Water for Injection.


  1. Zynyz Product Label

More about Zynyz (retifanlimab)

Related treatment guides

Further information

Always consult your healthcare provider to ensure the information displayed on this page applies to your personal circumstances.