Outcomes of patients with resected stage III/IV acral or mucosal melanoma, treated with adjuvant anti-PD-1 based therapy

Importance: Acral (AM) and mucosal melanomas (MM) are rare subtypes with a poor prognosis. In those with advanced disease, anti-PD-1 (PD1) therapy has reduced activity compared to that seen in non-acral cutaneous melanoma. Objective: To determine the efficacy of adjuvant PD1 in resected AM or MM. Design: An international, retrospective cohort study Setting: Data up to November 2021 collected from 20 centres across 10 countries. Participants: One hundred and ninety four patients with resected stage III or IV¹ AM or MM who received adjuvant PD1 were included and compared to matched patients from the Melanoma Institute Australia (MIA) database using a propensity score matching analysis. Main outcomes and measures: Recurrence-free survival (RFS), distant metastasis-free survival (DMFS) and overall survival (OS) were investigated. Results: Forty five of 139 (32%) AM and 9 of 55 (16%) MM patients completed adjuvant therapy. The main reason for early treatment cessation in both groups was disease recurrence: 51 (37%) and 30 (55%) in the AM and MM groups, respectively. In the AM group adjuvant PD1 was associated with a longer RFS [HR-0.69 (0.52–0.92, p = 0.0127)], DMFS [HR0.58 (0.38–0.89, p = 0.0134)] and OS [HR of 0.59 (0.38–0.92, p-value 0.0196)] when compared to the historical cohort. In the MM group there was no statistical difference in RFS [HR1.36 (0.69–2.68,p-value 0.3799], DMFS or OS. Conclusion and relevance: After adjuvant PD1, both AM and MM have a high risk of recurrence. Our data suggests a benefit to using adjuvant PD1 therapy in resected AM but not in resected MM. Additional studies to investigate the efficacy of adjuvant PD1 for MM are needed.