Hepatic tumor ablation with clustered microwave antennae: the US Phase II trial

Thermal ablation techniques have become important treatment options for patients with unresectable hepatic malignancies. Microwave ablation (MWA) is a new thermal ablative technique that uses electromagnetic energy to produce coagulation necrosis. We report outcomes from the first clinical trial in the United States using MWA and a 915 MHz generator.

Patients with unresectable primary or metastatic liver cancer were enrolled in a multi-institutional trial from March 2004 through May 2006. Demographic information, diagnosis, treatment, and outcomes were documented.

Eighty-seven patients underwent 94 ablation procedures for 224 hepatic tumors. Forty-two ablations (45%) were performed open, 7 (7%) laparoscopically, and 45 (48%) percutaneously. The average tumor size was 3.6 cm (range 0.5-9.0 cm). Single antenna ablation volumes were 10.0 ml (range 7.8-14.0 ml), and clustered antennae ablation volumes were 50.5 ml (range 21.1-146.5 ml). Outcome variables were measured with a mean follow-up of 19 months. Local recurrence at the ablation site occurred in 6 (2.7%) tumors, and regional recurrence occurred in 37 (43%) patients. With a mean follow-up of 19 months, 41 (47%) patients were alive with no evidence of disease. There were no procedure-related deaths. The overall mortality rate was 2.3%.

Microwave ablation is a safe and effective technology for hepatic tumor ablation. In our study, clustered antennae resulted in larger ablation volumes. Further studies with histological confirmation are needed to verify clinical results.