Ablation of colorectal liver metastasis: Interaction of ablation margins and RAS mutation profiling on local tumour progression-free survival.

OBJECTIVES: To investigate effects of ablation margins on local tumour progression-free survival (LTPFS) according to RAS status in patients with colorectal liver metastases (CLM). METHODS: This two-institution retrospective study from 2005-2016 included 136 patients (91 male, median age 60 years) with 218 ablated CLM. LTPFS was performed using the Kaplan-Meier method and evaluated with the log-rank test. Uni/multivariate analyses were performed using Cox-regression models. RESULTS: Three-year LTPFS rates for CLM with minimal ablation margin ≤10 mm were significantly worse than those with >10 mm in both mutant-RAS (29% vs. 48%, p=0.038) and wild-type RAS (70% vs. 94%, p=0.039) subgroups. Three-year LTPFS rates of mutant-RAS were significantly worse than wild-type RAS in both CLM subgroups with minimal ablation margin ≤10 mm (29% vs. 70%, p<0.001) and >10 mm (48% vs. 94%, p=0.006). Predictors of worse LTPFS were ablation margins ≤10 mm (HR: 2.17, 95% CI 1.2-4.1, p=0.007), CLM size ≥2 cm (1.80, 1.1-2.8, p=0.017) and mutant-RAS (2.85, 1.7-4.6, p<0.001). CONCLUSIONS: Minimal ablation margin and RAS status interact as independent predictors of LTPFS following CLM ablation. While minimal ablation margins >10 mm should be always the procedural goal, this becomes especially critical for mutant-RAS CLM. KEY POINTS: • RAS and ablation margins are predictors of local tumour progression-free survival. • Ablation margin >10 mm, always desirable, is crucial for mutant RAS metastases. • Interventional radiologists should be aware of RAS status to optimize LTPFS.