**5.2 Transarterial chemoembolization (TACE)**

Of all bridging therapies, TACE is the most validated and widely studied. TACE consists of occluding blood supply to the tumor or tumors and delivering a chemotherapy agent to the tumor via a branch of the hepatic artery which specifically supplies the tumor. During TACE, a chemotherapy agent such as doxorubicin or cisplatin in combination with lipiodol is injected, followed by an agent such as Gelfoam to occlude the tract. An advantage of TACE is that its use results in a high concentration of chemotherapy to the tumor or tumors; also it is useful in downstaging tumors larger than 3 cm (Pompili, 2005). A disadvantage of TACE is that it is less tolerated among patients with severe hepatic decompensation, such as in patients with ascites and impaired coagulopathy. Also, it is contraindicated in patients with portal vein thrombosis. A meta-analysis of several studies showed a median survival of 20 months with arterial embolization. In one study of 61 patients, the survival rate among those who received TACE at 1 and 4 years post transplant was 87.5% and 69.3%, respectively (Yao, 2008).

## **5.3 Radiation ablation (RFA)**

In RFA, a radiofrequency (RF) probe containing an alternating current of approximately 500 kHz and 131 degrees Fahrenheit, is inserted in or around a hepatic tumor via ultrasound guidance for approximately 4-6 minutes (Yao, 2008). Its mechanism of action is inducing thermal energy to the tissue via electromagnetic energy (Lee, 2007). Many centers use microwave ablation in contrast to RFA with similar or better results.In a study of 40 patients who underwent RFA, the rate of complete necrosis was 51.3% for nodules smaller than 3 cm and 14.3% for larger lesions (Pompili, 2005). In accordance with this study, TACE is perceived as more effective than RFA in treating lesions larger than 3 cm. The limitations of RFA are the anatomical location of the tumor, presence of large ascites, and multifocal HCC, in which cases it cannot be used.

#### **5.4 Percutaneous Ethanol Injection (PEI)**

In Percutaneous Ethanol Injection (PEI), ultrasound guidance is used to deliver ethanol over 4-8 sessions performed 1-2 times per week. Its mechanism of action is inducing local tumor necrosis as a result of cellular dehydration, protein denaturalization, and chemical occlusion of tumor vessels (Pompili, 2005). PEI is most effective in treating nodules <3 cm and is overall better tolerated than TACE. However, its major limitation is a high local recurrence rate, which can reach up to 43%. Other limitations include a long treatment time. Overall, RFA has better outcomes than PEI and is better tolerated. In one study, the overall 1-2 year survival rates were higher among patients treated with RFA versus PEI were 86% and 64% versus 77% and 43% respectively (Lencioni, 2010). PEI has similar limitations but less efficacy than RFA and is infrequently used in North America for treatment of HCC.
