In a clinical trial of 65 patients with metastatic or recurrent Merkel cell carcinoma who had not previously received systemic therapy for advanced disease, treatment with retifanlimab-dlwr (Zynyz™) achieved a 52% overall response rate and 18% complete response rate, leading the U.S. Food and Drug Administration (FDA) to grant it accelerated approval in March 2023.
Mechanism of Action
Programmed death receptor-1 (PD-1)–blocking antibody. Blocking the PD-1 receptor on T cells increases their activity and surveillance against tumors.
Adults with metastatic or recurrent Merkel cell carcinoma
500 mg every four weeks for up to two years or until patients experience disease progression or intolerable toxicity
Give as an IV infusion over 30 minutes. Do not administer as IV push or bolus.
Common adverse reactions reported in at least 10% of patients include fever and fatigue; pain in sites such as the back, bone, neck, and extremities; skin and subcutaneous tissue disorders, such as rash and itchiness; and gastrointestinal issues, such as nausea and diarrhea. The most common serious adverse reactions reported in at least 2% of the patients in the clinical trial were fatigue, arrhythmia, and pneumonitis.
Retifanlimab-dlwr may lead to unacceptable toxicity and a need to permanently discontinue the drug for toxicities such as atrial fibrillation, progression of chronic lymphocytic leukemia, demyelinating polyneuropathy, eosinophilic fasciitis, increased liver enzymes, infusion-related reactions, pneumonitis, pancreatitis, polyarthritis, and radiculopathy.
Closely monitor the following:
- Hematology (hemoglobin, platelets, neutrophil, lymphocyte) and chemistry (creatinine, calcium, AST, potassium, sodium, lipase, alkaline phosphatase, ALT) panels, specifically liver function testing
- Cardiac rhythm
- Respiratory status
- Symptoms of infusion-related reactions
Retifanlimab-dlwr can cause fetal harm if administered to pregnant patients. Assess pregnancy status in patients of reproductive potential.
Teach patients to self-monitor for adverse events and to contact their provider about signs of cough, chest pain, shortness of breath, diarrhea, severe abdominal pain, new or worsening rash, or signs of hepatitis, including dark-colored urine. Advise patients not to breastfeed during treatment and for four months following the final dose. Retifanlimab-dlwr can cause complications in patients who previously received an allogeneic stem cell transplant; counsel those patients to contact their provider immediately if they develop any signs of post-transplant complications or solid organ transplant rejection.
Retifanlimab-dlwr’s safety and effectiveness have not been established in pediatric patients. Of the patients studied in clinical trials, 79% were aged 65 or older and 37% were aged 75 or older. Data are insufficient to determine whether younger patients will respond differently from older adult patients.
Because of the risk for embryo-fetal toxicity, use hazardous drug precautions.
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