Long-term outcomes following microwave ablation for liver malignancies.

Background: Microwave ablation has emerged as a promising treatment for liver malignancies, but there are scant long-term follow-up data. This study evaluated long-term outcomes, with a comparison of 915-MHz and 24-GHz ablation systems. Methods: This was a retrospective review of patients with malignant liver tumours undergoing operative microwave ablation with or without liver resection between 2008 and 2013. Regional or systemic (neo)adjuvant therapy was given selectively. Local recurrence was analysed using competing-risk methods with clustering, and overall survival was determined from Kaplan-Meier curves. Results: A total of 176 patients with 416 tumours were analysed. Colorectal liver metastases (CRLM) comprised 81.0 per cent of tumours, hepatocellular carcinoma 8.4 per cent, primary biliary cancer 1.7 per cent and non-CRLM 8.9 per cent. Median follow-up was 20.5 months. Local recurrence developed after treatment of 33 tumours (7.9 per cent) in 31 patients (17.6 per cent). Recurrence rates increased with tumour size, and were 10, 93 and 33 per cent for lesions smaller than 1cm, 1-3cm and larger than 3cm respectively. On univariable analysis, the local recurrence rate was higher after ablation of larger tumours (hazard ratio (HR) 2.05 per cm; P<0.001), in those with a perivascular (HR 3.71; P=0.001) or subcapsular (HR 2.71; P=0.008) location, or biliary or non-CRLM histology (HR 2.47; P=0.036), and with use of the 24-GHz ablation system (HR 3.79; P=0.001). Tumour size (P<0.001) and perivascular position (P=0.045) remained significant independent predictors on multivariable analysis. Regional chemotherapy was associated with decreased local recurrence (HR 049; P=0.049). Overall survival at 4 years was 58.3 per cent for CRLM and 79.4 per cent for other pathology (P=0.360). Conclusion: Microwave ablation of liver malignancies, either combined or not combined with liver resection, and selective regional and systemic therapy resulted in good long-term survival. Local recurrence rates were low after treatment of tumours smaller than 3cm in diameter, and those remote from vessels.