Hypothesis: Although radiofrequency ablation (RFA) is increasingly an accepted option for patients with colorectal liver metastases, patients treated with resection vs RFA may have different tumor biology profiles, which might confound the relationship between choice of liver-directed therapy and outcome. Design: Retrospective review of a prospectively collected database. Setting: Major hepatobiliary center. Patients: Between January 1, 1999, and August 30, 2006, 258 patients with colorectal liver metastases underwent hepatic resection with or without RFA. Main Outcome Measures: Evaluation of outcome following resection alone, combined resection-RFA, and RFA alone using 3 statistical methods (paired-match control, Cox proportional hazards multivariate model, and propensity index) to identify and adjust for potential confounding variables. Results: The median number of hepatic lesions was 2, and the median size of the largest lesion was 3.0 cm. One hundred ninety-two patients (74.4%) underwent resection alone, 55 patients (21.3%) underwent resection-RFA, and 11 patients (4.3%) underwent RFA alone. Patients who underwent resection-RFA had significantly increased risk of extrahepatic failure at 1 year vs patients who underwent resection alone or RFA alone (P < .05). On matched control and multivariate analyses, patients who underwent RFA with or without resection had significantly worse disease-free and overall survival than patients who underwent resection alone. Propensity score methods revealed that the aggregate distribution of clinical risk factors for resection-RFA was markedly different from that for resection alone. This suggested a lack of comparability to allow for statistical comparisons in the assessment of causal inferences regarding the efficacy of RFA therapy. Conclusion: Although results of matched control and multivariate analyses suggested that RFA with or without resection was associated with worse outcome, propensity score methods revealed that the resection-RFA and resection-alone groups were different with regard to baseline tumor and treatment-related factors, making causal inferences about the efficacy of RFA unreliable.
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