Defining oligometastatic disease from a radiation oncology perspective : an ESTRO-ASTRO consensus document

Background: Recognizing the rapidly increasing interest and evidence in using metastasis-directed radiotherapy (MDRT) for oligometastatic disease (OMD), ESTRO and ASTRO convened a committee to establish consensus regarding definitions of OMD and define gaps in current evidence. Methods: A systematic literature review focused on curative intent MDRT was performed in Medline, Embase and Cochrane. Subsequent consensus opinion, using a Delphi process, highlighted the current state of evidence and the limitations in the available literature. Results: Available evidence regarding the use of MDRT for OMD mostly derives from retrospective, single-centre series, with significant heterogeneity in patient inclusion criteria, definition of OMD, and outcomes reported. Consensus was reached that OMD is largely independent of primary tumour, metastatic location and the presence or length of a disease-free interval, supporting both synchronous and metachronous OMD. In the absence of clinical data supporting a maximum number of metastases and organs to define OMD, and of validated molecular biomarkers, consensus supported the ability to deliver safe and clinically meaningful radiotherapy with curative intent to all metastatic sites as a minimum requirement for defining OMD in the context of radiotherapy. Systemic therapy induced OMD was identified as a distinct state of OMD. High-resolution imaging to assess and confirm OMD is crucial, including brain imaging when indicated. Minimum common endpoints such as progression-free and overall survival, local control, toxicity and quality-of-life should be reported; uncommon endpoints as deferral of systemic therapy and cost were endorsed. Conclusion: While significant heterogeneity exists in the current OMD definitions in the literature, consensus was reached on multiple key questions. Based on available data, OMD can to date be defined as 1–5 metastatic lesions, a controlled primary tumor being optional, but where all metastatic sites must be safely treatable. Consistent definitions and reporting are warranted and encouraged in ongoing trials and reports generating further evidence to optimize patient benefits

Completeness of Reporting Oligometastatic Disease Characteristics in Literature and Influence on Oligometastatic Disease Classification Using the ESTRO/EORTC Nomenclature

PURPOSE There is increasing evidence for the integration of locally ablative therapy into multimodality treatment of oligometastatic disease (OMD). To support standardised data collection, analysis, and comparison, a consensus OMD classification based on fundamental disease and treatment characteristics has previously been established. This study investigated the completeness of reporting the proposed OMD characteristics in literature and evaluated whether the proposed OMD classification system can be applied to the historical data. METHODS AND MATERIALS A systematic literature review was performed in Medline, Embase, and Cochrane, searching for prospective and retrospective studies, where stereotactic body radiation therapy was a treatment component of OMD. Reporting of the OMD characteristics as described in the European Organisation for Research and Treatment of Cancer/European Society for Radiotherapy and Oncology classification was analyzed, feasibility to retrospectively classify the proposed OMD states was investigated, and the effect of the categorization on overall survival (OS) was evaluated. RESULTS Our study shows incomplete reporting of the proposed OMD characteristics. The most fully reported characteristic was type of involved organs (88/95 studies); history of cancer progression was the least reported (not mentioned in 50/95 studies). Retrospective OMD classification of existing literature was only possible for 7 of the95 studies. With respect to categorization as de novo, repeat, or induced OMD, homogeneous patient cohorts were observed in 21 of the 95 studies, most frequently de novo OMD in 20 studies. Differences in OS at 2, 3, or 5 years were not statistically significant between the different states. OS was significantly influenced by primary tumor histology, with superior OS observed for prostate cancer and worst OS observed for non-small cell lung cancer. CONCLUSIONS The largely incomplete reporting of the proposed OMD characteristics hampers a retrospective classification of existing literature. To facilitate future comparison of individual studies, as well as validation of the OMD classification, comprehensive reporting of OMD characteristics using standardised terminology is recommended, as proposed by the European Organisation for Research and Treatment of Cancer/European Society for Radiotherapy and Oncology classification system and following European Society for Radiotherapy and Oncology -American Society for Radiation Oncology consensus