Retifanlimab Versus Avelumab for the Treatment of Metastatic Merkel Cell Carcinoma: A Matching-Adjusted Indirect Comparison Analysis

Merkel cell carcinoma (MCC) is a rare and aggressive skin cancer with poor prognosis and low survival rate. Retifanlimab and avelumab are monoclonal immune checkpoint inhibitor antibodies approved for metastatic or recurrent locally advanced MCC. The objective of this study was to analyze clinical outcomes with retifanlimab versus avelumab using a matching-adjusted indirect comparison (MAIC). Individual patient data from the phase 2 POD1UM-201 trial (NCT03599713, data cutoff July 2024) were used for the retifanlimab treatment group, and aggregate data from part B of the phase 2 JAVELIN Merkel 200 trial (NCT02155647) were used for the avelumab treatment group. Key prognostic factors/effect modifiers identified from published literature (age, Eastern Cooperative Oncology Group performance status, programmed cell death ligand 1 status, and disease characteristics) were selected for adjustment in the base case. Scenario analyses were also conducted, including additional covariates. An unanchored MAIC was conducted for overall survival (OS), progression-free survival (PFS), and overall response rate (ORR). After weighing characteristics, the effective sample size of the adjusted retifanlimab population was approximately 42 patients (47% of original sample size). In the base case analysis, weighted hazard ratio (95% CI) numerically favored retifanlimab versus avelumab for OS (0.800 [0.492, 1.303]) and was statistically significant for PFS (0.590 [0.396, 0.881]), with the latter driven by separation during the first 2 months of treatment. Weighted odds ratio numerically favored retifanlimab for ORR (1.871 [0.896, 3.908)]. Scenario analyses generally confirmed base case analyses. Results of this MAIC generally favored retifanlimab compared with avelumab, including a statistically significant difference in PFS and numerical trends in OS and ORR, building on the clinical evidence supporting retifanlimab for the treatment of metastatic MCC. These findings are subject to residual confounding and should be interpreted with caution. Merkel cell carcinoma is a rare, aggressive skin cancer. Once it spreads to other body parts, chemotherapy is often used for treatment but can be difficult for some patients to tolerate, especially if they are older. Avelumab and retifanlimab are newer treatments called immunotherapies. These treatments help the patient’s immune system recognize and attack cancer. Avelumab was approved in the USA and EU for Merkel cell carcinoma on the basis of results of the JAVELIN Merkel 200 clinical trial. Retifanlimab was more recently approved in the USA and EU on the basis of the results of the POD1UM-201 clinical trial. There is no trial directly comparing how well these drugs treat patients with Merkel cell carcinoma. The present study used a statistical method called a matching-adjusted indirect comparison analysis to adjust the JAVELIN Merkel 200 and POD1UM-201 trials to make them more similar. This allowed results from two separate trials for retifanlimab and avelumab to be compared. This indirect comparison of two separate trials suggests that patients treated with retifanlimab lived significantly longer with no disease progression versus avelumab. Results also generally favored retifanlimab for overall survival and tumor control. This adds to the clinical evidence supporting retifanlimab for patients with advanced Merkel cell carcinoma.