Impact of adjuvant immunotherapy on stage III acral malignant melanoma (ALM) in a Peruvian cancer center: A real-world experience.

e21541 Background: Acral malignant melanoma (AMM) is an aggressive and distinct subtype of melanoma associated with poor prognosis and reduced response to immunotherapy. Peru shows a high incidence of the acral subtype (~60%), similar to that reported in Asian populations. This study aimed to evaluate the clinical benefit of adjuvant immunotherapy with pembrolizumab in Peruvian patients with clinical stage III melanoma, with a focus on the acral subtype. Methods: A retrospective descriptive analysis was conducted in patients with clinical stage III malignant melanoma treated between 2021 and 2024. Clinicopathological data were obtained from medical records. Baseline characteristics were compared between acral and non-acral melanoma patients. Efficacy was assessed using recurrence-free survival (RFS). Statistical significance was set at p<0.05 using SPSS software. Survival curves were estimated using the Kaplan–Meier method. Results: A total of 48 patients were included. Median age was 59 years (range 27–83), and 94% had an ECOG performance status of 0–1. The most common primary site was the lower extremities (58%). Most patients presented with T4b tumors (65%, median Breslow thickness 7 mm), N1a disease (23%), and stage IIIC (65%) according to the AJCC 8th edition. The acral subtype accounted for 42% of cases. All patients received adjuvant anti-PD-1 therapy (pembrolizumab), and 19% also received radiotherapy. Male sex, presence of microsatellite disease, and higher nodal involvement were more frequent in acral compared with non-acral melanoma. After a median follow-up of 24 months, estimated 1-year RFS was 78% in non-acral patients and 69% in acral patients (p=0.86). Conclusions: This single-center study reports a high incidence of acral malignant melanoma among Peruvian patients with stage III disease. Clinical characteristics, 1-year RFS, and recurrence patterns were comparable between acral and non-acral subtypes. Adjuvant immunotherapy with pembrolizumab demonstrated clinical benefit in Peruvian patients with acral melanoma.