**1. Introduction**

58 Liver Tumors

Zhu, A.X., Stuart, K., Blaszkowsky, L.S., Muzikansky, A., Reitberg, D.P., Clark, J.W.,

*110*, 581-589.

Enzinger, P.C., Bhargava, P., Meyerhardt, J.A., Horgan, K.*, et al.* (2007). Phase 2 study of cetuximab in patients with advanced hepatocellular carcinoma. Cancer

> Cholangiocarcinoma is a type of liver cancer arising from the neoplastic transformation of the epithelial cells that line the intra- and extrahepatic bile ducts. Symptoms are usually evident only after blockage of the bile duct by the tumor. This is an extremely aggressive tumor, which has very poor prognosis and limited treatment options. Cholangiocarcinoma is relatively resistant to chemotherapy and radiation therapy leaving conventional treatment like surgery as the only option. Therefore, further understanding into the factors that are involved in tumor initiation, promotion and progression is required for designing alternate therapies to combat this devastating disease.

> The tumor microenvironment is one of the most important factors regulating tumor angiogenesis, tumor invasion and metastasis. The microenvironment is a well-recognized system that plays a key role in tumor progression. However, the mechanism through which tumor microenvironment regulates tumor progression and invasion is largely unknown. In this review, we discuss the current knowledge about the role of the tumor microenvironment in the pathogenesis of cholangiocarcinoma, the role of the tumor microenvironment in the classification of cholangiocarcinoma and efforts to develop treatments targeting the tumor microenvironment.
