Anti-PD1 checkpoint inhibitor therapy in acral melanoma: A multicentre study of 193 Japanese patients.

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Acral melanoma (AM) is an epidemiologically and molecularly distinct entity that is underrepresented in clinical trials on immunotherapy in melanoma. We aimed to analyze the real-world efficacy of anti-PD-1 antibodies in advanced AM.We retrospectively evaluated unresectable stage III or stage IV AM patients treated with an anti-PD-1 antibody in any line at 21 Japanese institutions between 2014 and 2018. The clinicobiologic characteristics, objective response rate (ORR, Response Evaluation Criteria in Solid Tumors), survival estimated using Kaplan-Meier analysis, and toxicity (Common Terminology Criteria for Adverse Events 4.0.) were analyzed to estimate the efficacy of the anti-PD-1 antibodies.In total, 193 patients (nail apparatus, 70; palm and sole, 123) were included in the study. Anti-PD-1 antibody was used as first-line therapy in 143 patients (74.1%). Baseline lactate dehydrogenase (LDH) was within normal level in 102 patients (52.8%). The ORR of all patients was 16.6% (complete response, 3.1%; partial response, 13.5%), and the median overall survival (OS) was 18.1 months. Normal LDH levels showed a significantly stronger association with better OS than abnormal levels (median OS 24.9 vs 10.7 months; P<0.001). Although baseline characteristics were similar between the nail apparatus and the palm and sole groups, ORR was significantly lower in the nail apparatus group (6/70 patients [8.6%] vs 26/123 patients [21.1%]; P=0.026). Moreover, the median OS in this group was significantly poorer (12.8 vs 22.3 months; P=0.03).Anti-PD-1 antibodies have limited efficacy in AM patients. Notably, patients with nail apparatus melanoma had poorer response and survival, making nail apparatus melanoma a strong candidate for further research on the efficacy of novel combination therapies with immune checkpoint inhibitors.

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