Role of adjuvant pembrolizumab in resected stage III melanoma: Real-world evidence from a Peruvian reference center.

e21546 Background: Stage III melanoma carries a high risk of recurrence after surgery. Adjuvant pembrolizumab has demonstrated improved outcomes in randomized clinical trials; however, Latin American (LATAM) populations remain underrepresented, and access to immunotherapy in public healthcare systems is limited. We evaluated real-world outcomes of adjuvant pembrolizumab compared with observation in a public national reference center in Peru. Methods: We conducted a retrospective cohort study of patients with resected AJCC stage III melanoma treated between 2021 and 2024. Patients were classified according to receipt of adjuvant pembrolizumab or observation (no adjuvant anti-PD-1 therapy due to limited access). Efficacy outcomes included recurrence-free survival (RFS), defined as time from definitive surgery to first recurrence, and overall survival (OS), defined as time from surgery to death from any cause; patients alive were censored at last follow-up. Survival estimates were generated using the Kaplan–Meier method, and hazard ratios (HRs) were calculated using Cox proportional hazards models (two-sided p < 0.05). Multivariable models were adjusted a priori for age, sex, ulceration, AJCC substage, and adjuvant radiotherapy. Results: A total of 81 patients were included (pembrolizumab n = 47; observation n = 34), with a median age of 62 years. After a median follow-up of 36 months, 3-year RFS was 87.1% in the pembrolizumab group versus 42.8% in the observation group (HR 0.51; 95% CI 0.24–1.06; p = 0.073). Three-year OS was 87.1% versus 36.4%, respectively (HR 0.17; 95% CI 0.05–0.50; p = 0.002). Exploratory subgroup analyses suggested an OS benefit among females, patients aged ≥50 years, those with stage IIIC disease, BRAF wild-type tumors, and patients receiving adjuvant radiotherapy. Improved RFS was observed in patients with BRAF wild-type tumors (p = 0.049) and in tumors without ulceration (p = 0.045). Conclusions: In this real-world Peruvian cohort, adjuvant pembrolizumab was associated with significantly longer overall survival and numerically longer recurrence-free survival compared with observation in resected stage III melanoma. The RFS benefit appeared more pronounced in BRAF wild-type tumors and in the absence of ulceration. These findings support the effectiveness of adjuvant anti-PD-1 therapy in routine clinical practice within resource-limited settings such as LATAM.