Efficacy of immune checkpoint inhibitor treatment for head and neck mucosal melanoma recurrence in patients treated with carbon-ion radiotherapy

Background: Carbon-ion radiotherapy (C-ion RT) is effective for head and neck mucosal melanoma (HN-MM), including radioresistant mucosal melanoma. Melanoma also responds effectively to immune checkpoint inhibitors (ICIs). Data on the efficacy and safety of ICIs for HN-MM are insufficient. Aims: To analyze the efficacy and safety of ICI salvage therapy in patients with HN-MM recurrence after C-ion RT. Methods and Results: This retrospective study analyzed the medical records of 52 patients with HN-MM treated with C-ion RT between 2012 and 2020. A dose of 57.6 or 64.0 Gy (relative biological effectiveness) was provided in 16 fractions. The primary endpoint was 3-year overall survival (OS) rate. The median follow-up time was 26.8 months for all patients. A total of 29 patients had local recurrence or distant metastasis, and 16 patients who received ICI therapy. The 3-year OS rate in the ICI group (n = 16) and best supportive care group (n = 13) were 53.8% and 0.0%, respectively (p = 0.837); the difference was not statistically significant. There were no deaths after 1 year among patients who underwent ICI therapy. No adverse events associated with C-ion RT were related to or exacerbated by ICI. Conclusion: ICI salvage therapy is effective and safe for patients with HN-MM recurrence after C-ion RT.