Survival Outcomes According to Metastatic Burden and Curative-Intent Resection in Metastatic Colorectal Cancer: a Retrospective Cohort study

Abstract Background Metastatic colorectal cancer (mCRC) encompasses a heterogeneous spectrum of disease presentations. Although advances in surgery and systemic therapy have expanded the technical feasibility and clinical indication of metastasectomy, identifying patients who are most likely to derive oncologic benefit from curative-intent resection (CIR) remains an important clinical challenge. This study evaluated survival outcomes according to metastatic burden, resection status, and treatment strategy in patients with mCRC. Methods In this single-center retrospective cohort study, patients diagnosed with mCRC between 2013 and 2023 who underwent surgery and/or chemotherapy were reviewed. Metastatic burden (MB) was stratified into three categories based on the number of metastatic lesions and the number of involved organs: low MB (≤ 3 metastases confined to a single organ), intermediate MB (4–6 metastases in a single organ or 2–6 metastases involving two organs), and high MB (≥ 7 metastases or involvement of three or more organs). Survival outcomes were compared according to MB and resection status. Among patients undergoing CIR (R0 or R1), upfront chemotherapy versus upfront surgery was compared in the low and intermediate MB groups, while in the high MB group, outcomes were compared according to whether CIR was achieved. Results MB and resection completeness were strongly associated with survival, with a graded relationship observed across categories. Survival was significantly worse in patients with seven or more metastatic lesions or three or more involved organs. While no significant difference was observed between upfront chemotherapy and upfront surgery in the low MB group, upfront chemotherapy was associated with more favorable outcomes in the intermediate MB group. In the high MB group, achievement of CIR was associated with significantly better survival than no CIR, regardless of treatment sequence. Conclusions These findings suggest that CIR could be considered for patients with up to six lesions and two organs and may also be beneficial even in patients with high MB, even when the outcome was R1 resection. Therapeutic strategy should be individualized, and the oncologic benefit of CIR should be discussed within a multidisciplinary framework.