Poor efficacy of anti PD-1 antibody based immunotherapy in patients with acral melanoma: results from the Spanish Melanoma Group (GEM) registry

Background: Acral melanoma (AM) is uncommon in non-Asian race. Limited data exist in non-Asian population. Objective: To analyze the activity of immunotherapy in patients diagnosed with AM in Spain. Methods: We analyzed clinical outcomes of AM in the nationwide Spanish Melanoma Group Registry. Results: 69 AM (17 stage III; 52 stage IV) and 724 cutaneous melanoma (CM) (190 stage III; 534 stage IV), predominantly non-Hispanic white. Regarding stage IV, AM patients were older (median 73.6 vs. 66.6 years, p = 0.001) and less often BRAF mutant (9.6% vs. 60.7%, p = 0.0001). First line immunotherapy (49 AM; 316 CM), response rate was 15.0% vs 39.1% (p = 0.0033), median progression free survival was 5.5 (95% CI 3.97–8.23) vs 15.3 months (95% CI 8.97- 26.3) (p = 0.001) and median OS was 17.3 (95% CI 13.32–39.97) versus 43.0 months (95% CI 30.81, NR) (p = 0.007), for AM and CM, respectively. Stage III AM were deeper (T4b in 52.9% vs. 25.3%, p = 0.02). In adjuvant anti PD-1-treated patients (14 AM; 156 CM) median RFS was 10.23 months (95% CI 6.0-NR) in AM versus NR (54.5-NR) in CM (p = 0.017) and 5 year OS was 36.1% vs. 75.8% (p = 0.034). Conclusions: Our data confirms a poor outcome of AM in the Spanish population.