Bridging Therapy for Liver Transplantation

Liver transplantation represents the best treatment option for patients with early-stage hepatocellular carcinoma, but due to organ shortage, most regions place limits on the size and number of lesions that qualify for this treatment. Locoregional treatment is often used with the objective of controlling tumor growth and preventing waitlist dropout. Historically, transarterial chemoembolization (TACE) and ablation techniques (radiofrequency ablation (RFA), among others) have been the most commonly used bridging techniques. Stereotactic body radiation therapy (SBRT), by delivering highly conformal radiation therapy, generally in 1–5 fractions, has emerged as a treatment modality with excellent local control and acceptable side effects, with similar outcomes following TACE or RFA, in similarly selected patients. The implementation of SBRT requires a multidisciplinary team that can address challenges in radiation treatment including liver motion, obtaining optimal imaging for planning, and image guidance. Compared to other local-regional therapies, SBRT has generally been reserved for patients with a deeper impairment in liver function. Moreover, when compared with other forms of bridge to transplant therapies, such as RFA or TACE, there is no significant difference in the dropout rates, postoperative complications, disease-free, and overall survival after liver transplantation. There are challenges regarding the use of SBRT as a bridge to transplant therapy. In addition to the need for advanced radiation therapy technologies, conventional imaging response assessment criteria such as RECIST and mRECIST have poor correlation with pathologic findings after SBRT in many reported series, and there is a need to develop more reliable radiologic response criteria in this setting. Promising technical advances such as adaptive radiotherapy, MRI image guidance, and proton beam therapy are being investigated in HCC patients with the goal of increasing the therapeutic ratio by reducing toxicity and improving tumor control.