Thermal Ablation Versus Surgical Resection for Intermediate-Size (3–5 cm) Colorectal Liver Metastases: Results from the Amsterdam Colorectal Liver Met Registry (AmCORE)

<b>Purpose</b>: Surgical resection has been the gold standard for colorectal liver metastases (CRLM) for decades. In recent years, thermal ablation has emerged as a first-line treatment option for small-size CRLM, while for intermediate-size lesions (3-5 cm), it is reserved for patients with unresectable disease. In this setting, thermal ablation has proven safe and effective, achieving durable local control (LC) in the majority of patients. This retrospective study compares oncological outcomes of thermal ablation versus surgical resection of intermediate-size (3-5 cm) CRLM. <b>Material and methods</b>: Patients treated with thermal ablation or surgical resection for intermediate-size CRLM between 2000 and 2025 were included. Baseline per-patient and per-procedure characteristics were compared across three groups: thermal ablation, surgical resection, and combined treatment. Per tumor characteristics were compared between thermal ablation and surgical resection. Primary outcomes included local tumor progression-free survival (LTPFS) and complication rates. Secondary outcomes were OS, distant progression-free survival (DPFS), LC, and length of hospital stay. Survival outcomes were analyzed using the Kaplan-Meier method; additionally, LTPFS was assessed using Cox proportional hazards regression models, with multivariable analyses performed to adjust for potential confounders. <b>Results</b>: A total of 320 patients with 448 metastases were included: 135 patients underwent thermal ablation, 156 underwent surgical resection, and 29 received combined treatment. LTPFS per tumor was significantly higher in the surgical resection group (HR 1.86, 95% CI 1.24-2.81, <i>p</i> = 0.0025), however, LC per tumor did not significantly differ amongst groups (HR 1.48, 95% CI 0.70-3.11, <i>p</i> = 0.307). Complication rates were significantly higher after resection (<i>p</i> < 0.001). OS and DPFS did not differ significantly between the three groups (<i>p</i> = 0.08 and <i>p</i> = 0.084). OS comparing only thermal ablation and resection was significantly lower in the thermal ablation group. Median hospital stay was 3, 5, and 7 days for the ablation, resection, and combined groups, respectively (<i>p</i> < 0.001). <b>Conclusions</b>: Thermal ablation offers a safe alternative to surgical resection for selected patients with intermediate-size (3-5 cm) CRLM, with higher treatment-site recurrence rates. With the option of repeat ablation, comparable local tumor control can be achieved. Improvements in local control with both modalities over time support the need for a prospective clinical trial.