Background: Immune checkpoint inhibitors (ICIs) have a lower efficacy in mucosal melanoma (MUM) than in cutaneous melanoma. The use of combination treatments with radiotherapy (RT) to improve the efficacy in MUM, however, requires further investigation.
Methods: We retrospectively evaluated 225 advanced MUM patients treated with anti-PD-1 monotherapy (PD1; 115) or anti-PD-1 + anti-CTLA-4 combination therapy (PD1+CTLA4; 42) with or without RT (56 and 12, respectively). Treatment efficacy was estimated by determining the objective response rate (ORR) and survival rate with the Kaplan-Meier analysis.
Results: The baseline characteristics between the two groups in each ICI cohort were similar, except for Eastern Cooperative Oncology Group performance status in the PD1 cohort. No significant differences in ORR, progression-free survival (PFS), and overall survival (OS) were observed between the PD1 alone and PD1+RT groups in the PD1 cohort (ORR 26% versus 27%, P > 0.99; median PFS 6.2 versus 6.8 months, P = 0.63; median OS 19.2 versus 23.1 months, P = 0.70) or between the PD1+CTLA alone and PD1+CTLA4+RT groups in the PD1+CTLA4 cohort (ORR 28% vs 25%, P = 0.62; median PFS 5.8 versus 3.5 months, P = 0.21; median OS 31.7 versus 19.8 months, P = 0.79). Cox multivariate analysis indicated that RT in addition to PD1 or PD1+CTLA4 did not have a positive impact on the PFS or OS.
Conclusions: A prolonged survival benefit with RT in combination with ICIs was not identified for advanced MUM patients, although RT may improve local control of the tumour and relieve local symptoms.
Keywords: Abscopal effect; Anti-CTLA-4 antibody; Anti-PD-1 antibody; Ipilimumab; Mucosal melanoma; Nivolumab; Pembrolizumab; Radiotherapy.
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