Comparison of efficacy between anti-PD-1 antibody monotherapy and nivolumab plus ipilimumab therapy as first-line immunotherapy for advanced mucosal melanoma in Japanese patients: A single-center, retrospective cohort study

Mucosal malignant melanoma (MMM) is a rare subtype of malignant melanoma with a more aggressive biological behavior than cutaneous melanoma (CM). Owing to its rarity, it is necessary to accumulate information on treatments, especially in Asians, in whom MMM occurs more frequently than in Caucasians. In this study, we investigated the efficacy and adverse events (AEs) of nivolumab plus ipilimumab therapy (NIVO+IPI) versus immune checkpoint inhibitor (ICI) monotherapy (PD-1) in Japanese patients with MMM. We reviewed patients with advanced or recurrent MMM who received ICIs as first-line systematic therapy between February 2012 and February 2024 at the Shizuoka Cancer Center. We enrolled a total of 57 patients: 10 (17.5%) were treated with NIVO+IPI, and 47 (82.5%) were treated with PD-1 as first-line systemic therapy. Objective response rates (ORR) did not differ significantly between the NIVO+IPI and PD-1 groups (40.0% vs 27.7%; p = 0.176). There was also no statistically significant difference in progression-free survival (PFS) (median PFS time: 4.3 months vs 9.9 months, log-rank test, p = 0.578) or overall survival (OS) (median OS time: 33.1 months vs. 22.8 months, log-rank test, p = 0.697) between the two groups. However, regarding AEs, grade >= 3 AEs leading to discontinuation of first-line treatment occurred in 80% of patients in the NIVO+IPI group and in 22.6% of patients in the PD-1 group (p = 0.002). No difference was found in the efficacy of NIVO+IPI therapy and anti-PD-1 antibody monotherapy as the first-line treatment for MMM in Japanese patients, but an increase in AEs was observed with combination therapy. This study suggests that patients with MMM may receive less benefit from NIVO+IPI than from PD-1.