Rates and Patterns of Recurrence After Microwave Ablation of Colorectal Liver Metastases: A Per Lesion Analysis of 416 Tumors in the Era of 2.45 GHz Generators.

BACKGROUND: For some patients with colorectal liver metastases (CRLMs), surgical resection of all visible disease can lead to long-term survival and even cure. When complete resection is not feasible, microwave ablation (MWA) can help achieve hepatic disease control. As modern 2.45-GHz MWA generators gain popularity, the characteristics of tumors most likely to benefit from this method remain unclear. This study aimed to evaluate local recurrence (LR) rates, patterns of recurrence, and factors contributing to treatment failure after 2.45-GHz MWA of CRLM. METHODS: Patients with CRLM who underwent operative 2.45-GHz MWA between 2011 and 2019 were identified in a prospectively maintained single-institution database. Recurrence outcomes were ascertained for each lesion by imaging review. Factors associated with LR were analyzed. RESULTS: The study enrolled 184 patients bearing 416 ablated tumors. Most of the patients (65.8%) had high clinical risk scores (3-5), and 165 (90%) underwent concurrent liver resection. The median tumor size was 10 mm. After a median follow-up period of 28.8 months, LR was observed in 45 tumors, and the cumulative incidence of LR at 24 months was 10.9% (95% confidence interval [CI], 8.0-14.3%]. In 7%, LR was the first recurrence site, often combined with recurrence elsewhere. The cumulative incidence of LR at 24 months was 6.8% (95% CI 3.8-11.0%) for tumors 10 mm in size or smaller, 12.4% (95% CI 7.8-18.1%) for tumors 11 to 20 mm in size, and 30.2% (95% CI 14.2-48.0%) for tumors larger than 20 mm. In the multivariable analysis, tumors larger than 20 mm with a subcapsular location were significantly associated with increased LR risk. CONCLUSIONS: Treatment of CRLM with 2.45-GHz MWA offers excellent local control at 2 years and is most successful for small tumors deep within the parenchyma.