Challenges in the use of the European Society for Radiotherapy and Oncology-European Organisation for Research and Treatment of Cancer oligometastatic disease classification system in ovarian cancer.

The oligometastatic disease classification system, developed within the European Society for Radiotherapy and Oncology (ESTRO)-European Organisation for Research and Treatment of Cancer (EORTC) OligoCare project, has been proposed for prognostic stratification and clinical trial design across solid tumours. Its application to ovarian cancer, however, is challenged by two disease-specific features: early and often diffuse peritoneal spread and the difficulty of lesion enumeration when peritoneal deposits are not discretely measurable. Historically, radiotherapy has had a restricted role in ovarian cancer, largely because effective doses cannot be safely delivered to diffuse peritoneal disease in a condition that is typically systemic at diagnosis. With the advent of more effective systemic therapies, stereotactic radiotherapy has emerged as a strategy to reach durable local control in selected patients with minimal metastatic burden. Adapting the ESTRO-EORTC oligometastatic disease classification system to this setting could improve patient stratification and therapeutic planning. We therefore advocate for a joint ESTRO-EORTC-European Society of Gynaecological Oncology initiative, in collaboration with the EORTC Gynecological Cancer Group, to define ovarian-specific rules for peritoneal disease, refine patient selection, and harmonise clinical practice and trial eligibility within a multidisciplinary framework.