Definition and treatment strategies for oligometastatic esophageal squamous cell carcinoma (OMESQ): a study protocol for global multidisciplinary consensus using the modified Delphi method

Background: The concept of oligometastatic disease (OMD) is an intermediate state in which local treatment may offer long-term disease control. While definitions and treatment strategies have been established for esophagogastric adenocarcinoma, they cannot be extrapolated to esophageal squamous cell carcinoma (ESCC) due to distinct biological behaviors and treatment strategies. Currently, no standardized global definition or treatment algorithm for oligometastatic ESCC (OMESQ) exists, which impedes the design of high-quality prospective trials. The OMESQ project aims to develop a global multidisciplinary consensus on the definition, diagnosis, and treatment of OMESQ. Methods: The OMESQ project is an international initiative led by the Japan Esophageal Oncology Group (JEOG) involving 58 centers across 14 countries or regions. The project consists of sequential sub-studies. OMESQ-1 is a systematic review that identifies current definitions and evaluates the survival impact of local treatment. The OMESQ-2 involves multidisciplinary tumor board discussions of real-life clinical cases to assess variability in diagnosis and treatment. The OMESQ-3 is a large-scale, multicenter, retrospective study evaluating the clinical outcomes and efficacy of conversion therapy in patients with five or fewer distant metastases. Integrating the findings from these three steps, the OMESQ-4 will establish a global consensus using a modified Delphi method with international experts, utilizing a 7-point Likert scale to evaluate statements. Finally, the OMESQ-5 is planned as a prospective international multicenter clinical trial based on the established consensus. Discussion: This comprehensive project will generate the first standardized consensus statement for the OMESQ. By harmonizing the definition, diagnosis, and treatment strategies, the OMESQ consensus will improve consistency in clinical practice and serve as the foundation for future prospective trials aimed at improving patient survival rates.