Outcomes of adjuvant lymph node field radiotherapy and immunotherapy for stage III melanoma.

Purpose: With the promising results of immunotherapy in patients with stage III melanoma, the role of adjuvant radiotherapy after resection and complete lymph-node dissection must be reassessed. We evaluate the outcomes and safety of adjuvant radiotherapy and immunotherapy compared to immunotherapy only in patients with resected stage III melanoma.

Patients and methods: This retrospective and single institution study included patients treated for a stage III melanoma with complete lymph-node dissection and adjuvant immunotherapy from January 2019 to December 2022. The radiotherapy associated with immunotherapy group was defined by completion of immunotherapy and adjuvant radiotherapy in the lymph-node dissection area. The primary endpoint was disease-free survival. The secondary endpoints were locoregional progression, incidence of adverse events grade 3 or above and disease-free survival rate in patients with high risk of locoregional recurrence.

Results: Thirty-three patients were included. Among them, twelve received adjuvant lymph-node field radiotherapy. The median duration of follow-up was 17months (range: 8-45months). Patients receiving radiotherapy and immunotherapy had a significantly higher disease stage and more frequent extracapsular extension. At 12months, the disease-free survival rate was 66.7% for the patients receiving immunotherapy alone (95% CI: 42.5-82.5%) and 83.3% for those receiving radiotherapy and immunotherapy (95% CI: 48.2-95.6%; P=0.131). The locoregional progression rate was 24% in patients receiving immunotherapy and 8% in patients receiving immunotherapy and radiotherapy (P=0.379). After adjuvant treatment, 6% of patients developed grade 3 or above immunotherapy-related events and none developed grade 3 or above radiation-related adverse events.

Conclusion: In patients with stage III melanoma, adjuvant lymph-node field radiotherapy combined with immunotherapy seems to be associated with longer disease-free survival, with acceptable tolerance. However, these results need to be confirmed by long-term and prospective studies.