Liver-Directed Therapies in Neuroendocrine Tumors

The liver is the most frequent metastatic site of neuroendocrine neoplasms, especially those of gastroenteropancreatic origin. The presence of liver metastases is a major negative factor altering both the quality of life and the long-term prognosis of patients, justifying their dedicated treatment. Among all available treatment options, a variety of image-guided liver-directed therapies can be considered, including percutaneous thermal ablation and intra-arterial treatments. Ablation is indicated for oligometastatic small-sized tumors either in non-surgical patients or in association with surgery (parenchyma-sparing approach). Intra-arterial treatments are commonly used in liver only or liver-dominant disease and include transarterial chemoembolization (TACE), bland embolization (TAE), and radioembolization (TARE). TACE/TAE is associated with reported overall survival of 3–4 years and objective response rate up to 75%. The benefit of TACE over TAE is unclear, but evidence suggests it might exist in pancreatic NETs. The results of TARE appear similar to that of TACE/TAE, but this technique needs to be further evaluated, especially in terms of long-term toxicity. Indications of image-guided liver-directed therapy in the treatment of NET liver metastases need to be refined, considering the extent of the liver burden, the metastastic pattern, the location of the primary tumor, tumor differentiation, and tumor proliferative activity. One advantage of these treatments is to save the benefit and the toxicity of systemic therapy for more advanced stage of the disease. This chapter addresses the various roles, technicalities, clinical efficacy and safety of thermal ablation (radiofrequency, microwave and cryotherapy), and transarterial procedures (bland embolization, chemoembolization and radioembolization) as liver-directed therapies.