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