ESTRO 2025 - Abstract Book

S1564

Clinical – Mixed sites & palliation

ESTRO 2025

Radiotherapy, Institute Of Oncology Ljubljana and Faculty of Medicine, University of Ljubljana, Ljubljana, Slovenia. 13 ., Policlinico Universitario Campus Bio-Medico di Roma, Rome, Italy. 14 ., Università Campus Bio-Medico di Roma, Rome, Italy. 15 Department of Radiation Oncology, Iridium Network, Antwerp, Belgium. 16 Radiation Oncology, Catharina Ziekenhuis, Eindhoven, Netherlands. 17 ., Radiotherapiegroep, Deventer, Netherlands. 18 Department of Radiation Oncology, Bern University Hospital, University of Bern, Bern, Switzerland. 19 Radiation Oncology, Hospital General Universitario Santa Lucia, Cartagena, Spain. 20 European Organisation for Research and Treatment of Cancer (EORTC), Headquarters, Brussels, Belgium. 21 Department of Human Structure and Repair, Universitair Ziekenhuis Gent, Gent, Belgium Purpose/Objective: Stereotactic body radiotherapy (SBRT) is the most frequently used metastasis-directed treatment for patients with oligometastatic cancer in prospective trials and most studies reported favorable therapeutic ratio. However, uncertainties exist in patients treated with concurrent SBRT and systemic therapy, because most studies have been too small to perform subgroup analyses with respect to metastasis location and type of systemic therapy. This interim analysis of the OligoCare project aims to analyze potential association between post-SBRT severe adverse events (AE) and concurrent systemic therapy. Material/Methods: OligoCare is a pragmatic prospective observational cohort study of the E²-RADIatE project, a collaboration between ESTRO and EORTC. Patients are eligible irrespective of the oligometastatic state, if all lesions can be treated with radical intent. Radical radiotherapy must be a component of treatment. The analysis is based on a snapshot of the E²-RADIatE OligoCare database on August 27 2024. Endpoints are post-SBRT grade 3+ AE, reported between the start of SBRT until cut-off date of June 30 2024. Results: Between July 2019 and June 2024, 51 institutions enrolled 2335 patients into the OligoCare cohort and 2294 patients were eligible for this analysis. Patients were treated for oligometastatic non-small cell lung cancer (NSCLC; 461), breast cancer (BC; 324), colorectal cancer (CRC; 453) or prostate cancer (PC; 1056). Concomitant systemic therapy was used in 779 (34%) patients (NSCLC: 32.3%; BC: 52.8%; CRC: 11.3%; PC: 38.6%), and type of systemic therapy was chemotherapy (132), targeted therapy (16), immunotherapy (81), antihormonal therapy (528) or other (3). With a median follow-up of 24.1 months (95%CI 23.8-24.4), grade 3+ AEs were observed in 27 patients (1.2%), including grade 3 in 21 patients, grade 4 in 1 patient, and grade 5 in 5 patients. Grade 3+ AEs were observed in 11 (1.4%) and 16 (1.1%) patients treated with and without systemic therapy (Table 1). Grade 5 AE were observed in two and three patients, respectively, with a median time of 6.3 months (range 2.7 – 11.6). Grade 3+ AEs were observed in 5 (3.8%) patients treated with concomitant chemotherapy, 4 (3.4%) patients treated with targeted therapy (116), 1 (1.2%) treated with immunotherapy and 3 (0.6%) treated with antihormonal therapy (Table 2), and in 6.5% and 1.1% of patients treated for cranial and extracranial metastases, respectively.