Prognostic Significance of the ESTRO/EORTC Classification of Oligometastatic Disease for Colorectal Cancer Patients With Uncommon Metastases Treated With Definitive Radiotherapy

Background/Aim: Prognostic significance of ESTRO/EORTC classification (Lancet Oncol. 21:e18-e28) for colorectal cancer patients with oligometastatic disease at uncommon sites unfit for surgery is unclear. Patients and Methods: We conducted a retrospective study of colorectal cancer patients with post-surgical oligometastatic disease at uncommon sites treated with definitive radiotherapy. We identified eligible patients via in-house databases. Clinical, disease, treatment, and outcome data were obtained through medical-record review, with classifications determined by consensus among the attending physicians. Overall survival (OS) and progression-free survival (PFS) were estimated using the Kaplan-Meier method. Cox regression models were used to investigate the potential prognostic factors including the ESTRO/EORTC classification. We also estimated the incidence of local progression. Results: We identified 59 eligible patients treated from Dec 2012 to Sep 2025. After a median follow-up of 28 months (range=3-145 months), the 5-year OS, PFS, and incidence of local progression were 24%, 10%, 66% respectively. Induced oligoprogression was associated with inferior PFS (adjusted hazard ratio 3.82, p=0.004) but not OS. Conclusion: ESTRO/EORTC classification was associated with outcomes for colorectal cancer patients with oligometastatic disease at uncommon sites treated with definitive radiotherapy. Future studies are needed to validate our findings.