2126 - Role of Retreatment with Stereotactic Ablative Body Radiotherapy (SABR) in Oligorecurrent Mesothelioma: A Retrospective Monocentric Study

F. Gessoni¹, F. Matrone¹, G. Pirrone², J. Polesel³, L. Vinante¹, A. Caroli¹, A. A. M. Donofrio¹, F. Bertini¹, G. Fanetti¹, F. Navarria¹, G. Malfatti¹, L. Barresi², A. Drigo², M. Mascarin¹, and A. Revelant¹; ¹Department of Radiation Oncology, Centro di Riferimento Oncologico of Aviano, Aviano, Italy, ²Division of Medical Physics, Centro di Riferimento Oncologico Aviano IRCCS, Aviano, Italy, ³Department Cancer Epidemiology, Centro di Riferimento Oncologico of Aviano, Aviano, Italy

Purpose/Objective(s): Limited second-line therapeutic options are available in Malignant Pleural Mesothelioma (MPM). In this patients Stereotactic Ablative Body Radiotherapy (SABR) could postpone the begin of a second-line systemic therapy in those with radiological findings of oligorecurrent disease. Primary aim of our study was to determine the time to second-line systemic therapy (TTST) in this setting. In this population we also evaluated Progression-Free Survival (PFS) and Overall Survival (OS). Materials/

Methods: All patients with MPM enrolled in this analysis were previously treated with platinum-based chemotherapy, surgery (thoracoscopic biopsy, pleural decortication or pleurectomy plus decortication), Radical Hemithoracic Radiotherapy (RHR). An additional inclusion criteria was a minimum follow-up of 6 months. During the first radiotherapy course, all the patients received a total dose of 50 Gy in 25 fractions with a concomitant boost of 60 Gy to PET/TC positive macroscopic residual disease. Patients showing an oligorecurrent ipsilateral pleural disease (defined as radiological evidence of lesion numbers = 3) underwent SABR re-irradiation following a fractionation scheme of 25-30 Gy in 3-5 daily fractions. TTST was defined as the time between the first day of SABR retreatment and the first day of second-line systemic treatment. PFS was defined as the time between SABR re-irradiation and the first radiological finding of disease progression, while OS was defined as the time between SABR retreatment and the patient death. All considered outcomes were calculated with Kaplan-Meier method. Toxicities of RHR and SABR re-irradiation were assessed with Common Terminology Criteria for Adverse Events (CTCAE) Vers. 5.0.
Results: Twenty-two patients were treated between January 2011 and December 2022, with a median follow-up of 11.4 months (6-36 months). At the time of analysis, only 5 patients were alive, including 2 patients with no evidence of disease. After SABR re-irradiation, only 9 patients developed a plurimetastatic disease (3 patients with extensive local progression and 6 patients with distant progression) and started a second-line systemic treatment. Median TTST was 10.2 months [Q1-Q3: 4.8-17.1]. PFS rates at 6,12, 36 months were 71.8% [47.6%-86.2%], 33.5% [15.0%-53.3%] and 14% [3.6%-32.2%], respectively. OS rates at 6,12, 36 months were 95.2% [70.7%-99.3%], 56.4% [32.8%-74.5%], 27.4% [9.5%-48%], respectively. Only one patient developed acute G2 gastrointestinal toxicity while no other acute or late toxicities were reported.
Conclusion: Results of a very homogeneous population were reported in this study. SABR re-irradiation in patients with oligorecurrent MPM appears to be safe and useful to postpone second-line systemic treatment. Further prospective studies and randomized trials are needed to support our findings.