Retifanlimab is used to treat a type of skin cancer called Merkel cell carcinoma in adults, when the cancer has spread to other parts of the body (metastatic) or returned.

Retifanlimab may also be used for purposes not listed in this medication guide.

Call your doctor at once if you have symptoms such as: cough, flu symptoms, muscle pain or weakness, vision changes, chest pain, trouble breathing, severe stomach pain or diarrhea, rash, swelling in your ankles, increased or decreased urination, blood in your urine or stools, weight changes, hair loss, dark urine, or jaundice (yellowing of your skin or eyes).

Follow all directions on your prescription label and read all medication guides or instruction sheets.

Retifanlimab is injected into a vein by a healthcare provider over 30 minutes. This medicine is usually given every 4 weeks.

Your blood will need to be tested often.

Usual Adult Dose for Merkel Cell Carcinoma:

Dose: 500 mg IV every 4 weeks
-Administer as IV infusion over 30 minutes until disease progression, unacceptable toxicity, or up to 24 months

Comments:
This indication is approved under accelerated approval based on tumor response rate and duration of response. Continued approval for this indication may be contingent upon verification and description of clinical benefit in confirmatory trials.

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

Tell your doctor if you have or have ever had:

• immune system problems such as ulcerative colitis, Crohn's disease, or lupus;

• a nervous system condition, such as myasthenia gravis or Guillain-Barré syndrome;

• received an organ transplant;

• received or plan to receive a stem cell transplant that uses donor stem cells; or

• received radiation treatment to your chest area.

You may need to have a negative pregnancy test before starting this treatment.

May harm an unborn baby. Do not use if you are pregnant. Use effective birth control while using retifanlimab and for at least 4 months after your last dose. Tell your doctor if you become pregnant.

Do not breastfeed while using retifanlimab, and for at least 4 months after your last dose.

Call your doctor for instructions if you miss an appointment for your retifanlimab injection.

In a medical setting an overdose would be treated quickly.

Follow your doctor's instructions about any restrictions on food, beverages, or activity.

Get emergency medical help if you have signs of an allergic reaction: hives, difficult breathing, swelling of your face, lips, tongue, or throat.

Some side effects may occur during the injection. Tell your medical caregiver if you feel dizzy, nauseated, light-headed, itchy, sweaty, or have a headache, chest tightness, back pain, trouble breathing, or swelling in your face.

Retifanlimab may cause serious side effects. Call your doctor at once if you have:

• cough, shortness of breath, chest pain;

• irregular heartbeat;

• confusion, drowsiness, memory problems, changes in mood or behavior, stiff neck, problems with balance, tingling or numbness in your arms or legs;

• vision changes, sensitivity to light, eye pain;

• severe muscle pain or weakness, muscle cramps;

• bruising;

• severe stomach pain or tenderness, diarrhea, bloody or tarry stools;

• blistering or peeling of the skin, rash, itching;

• genital area, mouth, nose, or throat sores or ulcers;

• flu-like symptoms;

• feeling sick or uneasy, with pain or swelling near your transplanted organ;

• low red blood cells (anemia)--pale skin, tiredness, feeling light-headed or short of breath, cold hands and feet;

• liver problems--loss of appetite, nausea, vomiting, stomach pain (upper right side), tiredness, itching, dark urine, clay-colored stools, jaundice (yellowing of the skin or eyes);

• kidney problems--little or no urination, red or pink urine, swelling in your feet or ankles; or

• signs of a hormonal disorder--unusual headaches, vision problems, feeling light-headed or very tired, rapid heartbeats, mood or behavior changes, hoarse or deepened voice, increased hunger or thirst, increased urination, constipation, hair loss, sweating, feeling cold, muscle pain, weight gain, or weight loss.

Your treatment with retifanlimab may be delayed or permanently discontinued if you have certain side effects.

Common side effects of retifanlimab may include:

• tiredness;

• itching, rash;

• fever;

• muscle and bone pain; or

• nausea, diarrhea.

This is not a complete list of side effects and others may occur. Call your doctor for medical advice about side effects. You may report side effects to FDA at 1-800-FDA-1088.

Other drugs may affect retifanlimab, including prescription and over-the-counter medicines, vitamins, and herbal products. Tell your doctor about all other medicines you use.