Radiofrequency ablation of the liver: current status.

H epatocellular carcinoma (HCC) and metastases from colorectal carci­ noma are the two most common malignant tumors to affect the liver. When these tumors are left untreated, the prognosis for both is dismal, with essentially 100% mortality at 5 years. Conventional therapies such as systemic chemotherapy or radiation have proven ineffec­ tive. Surgical resection of the tumors is consid­ ered the only potentially curative therapy [1–4]. Successful resection of targeted tumors with negative tumor margins is achieved in approxi­ mately 80–90% of patients undergoing hepatic resection [5–7]. Unfortunately, surgical resec­ tion has many factors limiting its overall useful­ ness. Of all patients presenting with a malignant hepatic tumor, few are surgical candidates. Con­ traindications to hepatic resection include too many tumors, tumors in unresectable locations, insufficient hepatic reserve to tolerate resection, and other medical conditions that make the pa­ tient a poor surgical risk. It has been estimated that only 5–15% of patients with HCC or he­ patic metastases are eligible for resection [1–4]. For those patients who undergo hepatic resec­ tion, there is considerable postoperative morbid­ ity—a small but real risk of death related to the operation—significant monetary expense, and only a modest improvement in long-term prog­ nosis. The 5-year survival rate for patients un­ dergoing resection of HCC or hepatic metastases is only 20–40% [1–3]. Most patients die from recurrent hepatic tumors. Although in some instances surgery may be repeated to re­ sect recurrent tumor, at most institutions hepatic resection is a “one-shot” therapy. In light of these shortcomings, an effective, minimally in­ vasive technique is needed for treating these tumors—one that can be repeated as necessary to treat recurring tumor. A number of alternative therapies have been used for the treatment of malignant hepatic tu­ mors. These include chemoembolization, etha­ nol injection therapy, and thermal ablation techniques. Chemoembolization has been studied extensively and is often reserved for patients with unresectable hepatic tumors [8, 9]. Ethanol injection therapy has gained fair in­ ternational acceptance as a safe, inexpensive, and effective therapy for small HCC tumors [10, 11]. However, it has failed to generate much enthusiasm in the United States. This lack of enthusiasm is based in part on the need to perform multiple consecutive therapeutic sessions to completely kill even the smallest HCC tumor and the fact that the technique is typically performed under sonographic guid­ ance [11]. Furthermore, ethanol injection ther­ apy has been shown to be ineffective for the treatment of colorectal metastases [12]. Thermal ablation techniques for the treat­ ment of malignant hepatic tumors include both freezing (cryoablation) and heating (radiofre­ quency, microwave, laser, and high-intensity focused sonography) techniques. Of these tech­ niques, cryoablation has been the most exten­ sively investigated [13, 14]. The two advantages of cryoablation over surgical resection are that it can be used to treat liver tumors that, by number or location, are not surgically resectable, and that it is associated with diminished morbidity and mortality relative to resection. The overall prognosis for patients undergoing cryoablation is reported to be the same as for hepatic resec­ tion. However, the limitations of cryoablation are similar to the limitations of hepatic resec­ tion—namely, it is invasive, with a laparotomy being performed in most cases [14]. During the last 10 years, considerable inter­ est has developed in the thermal ablation tech­ niques that produce heat. Methods that are being investigated include microwave, laser, high-intensity focused ultrasound, and radiofre­ quency ablation. Most of the research on micro­ wave ablation has been performed in Japan, with minimal experience or knowledge of the technique outside that country [15, 16]. Laser ablation has been tested most rigorously outside the United States [17–19]. One group of Ger­ man researchers, Vogl et al. [19], claim that the technique is highly effective for the treatment of both HCC and colorectal metastases. However, one of the primary investigators of laser ablation in England has essentially abandoned the tech­ nique in favor of radiofrequency ablation [20]. High-intensity focused ultrasound has been shown to be successful in ablating hepatic tu­ mors in animal models but has not been used to treat liver tumors in humans [21]. Overall, the interest and enthusiasm for radiofrequency ther­ mal ablation has far exceeded that for either mi­ crowave or laser ablation. This article will