Margin Size is an Independent Predictor of Local Tumor Progression After Ablation of Colon Cancer Liver Metastases

This study was designed to evaluate the relationship between the minimal margin size and local tumor progression (LTP) following CT-guided radiofrequency ablation (RFA) of colorectal cancer liver metastases (CLM). An institutional review board-approved, HIPPA-compliant review identified 73 patients with 94 previously untreated CLM that underwent RFA between March 2003 and May 2010, resulting in an ablation zone completely covering the tumor 4-8 weeks after RFA dynamic CT. Comparing the pre- with the post-RFA CT, the minimal margin size was categorized to 0, 1-5, 6-10, and 11-15 mm. Follow-up included CT every 2-4 months. Kaplan-Meier methodology and Cox regression analysis were used to evaluate the effect of the minimal margin size, tumor location, size, and proximity to a vessel on LTP. Forty-five of 94 (47.9 %) CLM progressed locally. Median LTP-free survival (LPFS) was 16 months. Two-year LPFS rates for ablated CLM with minimal margin of 0, 1-5 mm, 6-10 mm, 11-15 mm were 26, 46, 74, and 80 % (p < 0.011). Minimal margin (p = 0.002) and tumor size (p = 0.028) were independent risk factors for LTP. The risk for LTP decreased by 46 % for each 5-mm increase in minimal margin size, whereas each additional 5-mm increase in tumor size increased the risk of LTP by 22 %. An ablation zone with a minimal margin uniformly larger than 5 mm 4-8 weeks postablation CT is associated with the best local tumor control.