T he incidence of hepatocellular carcinoma (HCC) recurrence following surgical resection and locoregional therapy (LRT) performed with curative intent is high. Three-year local progression rates after radiofrequency ablation (RFA) vary widely between institutions, ranging from 3.2% to 21.9%. [1][2][3] Recurrence rates of 50% to 70% (of which 80% to 90% are intrahepatic) have been reported five years after hepatectomy. 4 Such recurrences constitute a significant cause of late mortality.Trans-arterial therapies have traditionally been recommended in those with large tumors or multifocal disease (intermediate stage). Since some patients' treatment goals are palliative, it is common for patients to undergo more than one treatment, sometimes using combination therapies to achieve disease control. 5 The reported rates of residual disease post-trans-arte- PURPOSEThe purpose of this study was to analyze and compare the outcomes of percutaneous microwave ablation (MWA) when used as a primary vs. secondary treatment for hepatocellular carcinoma (HCC). METHODSThe clinical data of 192 patients with HCC treated with MWA between January 2012 and July 2021 were reviewed retrospectively, with 152 patients being treatment naïve (primary treatment) vs. 40 who had residual or recurrent disease following previous trans-arterial chemoembolization or trans-arterial radioembolization (secondary treatment). The primary outcomes were primary technical efficacy, 1-and 3-year local recurrence-free survival (RFS) and overall survival (OS), local recurrence rates, and adverse events. Pre-and post-intervention liver function tests were compared using a Wilcoxon signed rank test. Univariate and multivariate analyses were also performed, looking at prognostic factors associated with OS and local RFS. RESULTSThere was no significant difference in 1-year local RFS (primary 93.6% vs. secondary 93.7; P = 0.97) and 3-year local RFS (primary 80.6% vs. secondary 86.5%; P = 0.37) rates. There was no significant difference in 1-year OS (primary 82.4% vs. secondary 86.6%; P = 0.51) and 3-year OS (primary 68.3% vs. secondary 77.4%; P = 0.25) between the two groups. The local recurrence rate (primary 9.8% vs. secondary 14.6%; P = 0.37), primary technical efficacy (primary 96.2% vs. secondary 95%; P = 0.73), and adverse events (primary 8.0% vs. secondary 11.6%; P = 0.45) were also similar between the two groups. CONCLUSIONMicrowave ablation is safe and effective as a secondary treatment for patients with HCC in a clinical salvage scenario and should be utilized more frequently.