ESTRO 2025 - Abstract Book

S1683

Clinical - Sarcoma & skin cancer & malignant melanoma

ESTRO 2025

2198

Digital Poster Efficacy of Radiotherapy in Stabilization of Oligoprogressive Lesions of Malignant Melanoma Treated with Immunotherapy Martin Palkovsky 1,2 , Alzbeta Hlodakova 1,2 , Jindrich Kopecky 3 , Marek Pasek 4,2 , Jiri Svec 1,2 , Monika Arenbergerova 4,2 , Petr Arenberger 4,2 , Renata Soumarova 1,2 1 Department of Oncology, University Hospital Kralovske Vinohrady, Prague, Czech Republic. 2 Third Faculty of Medicine, Charles University, Prague, Czech Republic. 3 Department of Clinical Radiotherapy and Oncology, University Hospital in Hradec Kralove, Hradec Kralove, Czech Republic. 4 Department of Dermatology and Venereology, University Hospital Kralovske Vinohrady, Prague, Czech Republic Purpose/Objective: This study aims to evaluate the effectiveness of radiotherapy (RT) in stabilizing oligoprogressive disease (OPD) in melanoma patients undergoing immunotherapy. We hypothesize that the efficacy of RT in disease stabilization is influenced by factors such as dose, fractionation, metastatic burden, and the timing of OPD onset relative to immunotherapy initiation. Material/Methods: A retrospective, bicentric observational study was conducted at two Czech university hospitals. Inclusion criteria encompassed metastatic melanoma patients undergoing immunotherapy with checkpoint inhibitors who developed OPD between January 2018 and May 2023. Exclusion criteria included CNS involvement, discontinuation of systemic therapy during or after RT, and treatments other than immune checkpoint inhibitors. Patients were stratified based on RT initiation timing (<6 months or >6 months from immunotherapy start) to assess primary and acquired resistance. Results: The study included 34 patients, with RT administered for extracranial OPD. Among these, local control was achieved in 22 patients (4 complete responses, 10 partial responses, and 8 stable diseases). The overall survival (OS) and progression-free survival (PFS) were significantly longer in patients receiving RT more than six months after immunotherapy initiation (p = 0.028). Patients with fewer than five irradiated lesions experienced better PFS, although OS was not significantly impacted. Higher doses of RT (>40 Gy EQD2) correlated with improved local control. Not reaching EQD2 >40 Gy was significantly associated with in-field progression after RT, lesions irrupted to EQD2 >40 Gy tended to reach complete response, however, the trend was not statistically significant. Conclusion: RT is a viable option for stabilizing OPD in melanoma patients treated with immunotherapy, especially when administered later in the treatment course. Improved OS and PFS outcomes suggest that delayed OPD may indicate acquired resistance, which benefits from RT. Future studies should refine RT parameters and patient selection criteria to optimize clinical outcomes.

Keywords: melanoma, oligoprogression, radiotherapy