**3.2.1 Cancer-associated fibroblasts in cholangiocarcinoma**

Cancer-associated fibroblasts are the predominant cell type in the stroma of cholangiocarcinoma tumors (Sirica et al. 2009). Increased -smooth muscle actin-positive fibroblasts were correlated with shorter survival times and larger tumor sizes in resected cholangiocarcinoma tissue (Chuaysri et al. 2009; Okabe et al. 2009). The origin of these cancer-associated fibroblasts is unknown, although a number of possibilities have been suggested, including hepatic stellate cells (Okabe et al. 2009), portal fibroblasts (Dranoff and Wells 2010) or circulating bone marrow-derived precursor cells (Shimoda et al. 2010). Given the apparent heterogeneous population of cancer-associated fibroblasts observed in cholangiocarcinoma tumors, it is highly likely that these fibroblasts are derived from more than one source. Recently, researchers have performed genetic screening to determine the differences in gene expression between cholangiocarcinoma-derived cancer-associated fibroblasts and non-malignant liver fibroblasts and showed a number of genes associated with angiogenesis, cell proliferation and motility (Utispan et al. 2010). In particular, periostin, a cell adhesion molecule, was shown to be significantly upregulated correlating with shorter survival time in patients and increased cell proliferation and invasive properties *in vitro* (Utispan et al. 2010). Another gene specifically expressed by cholangiocarcinoma-derived cancer-associated fibroblasts is the extracellular matrix protein tenascin-C (Aishima et al. 2003; Iguchi et al. 2009). This gene was expressed predominantly in the stroma near the invasion front of the tumor (Aishima et al. 2003) and was associated with poor prognosis in intrahepatic cholangiocarcinoma (Aishima et al. 2003; Iguchi et al. 2009). Furthermore, the expression of thrombospondin-1 by cancer-associated fibroblasts correlated with increased metastatsis (Kawahara et al. 1998; Tang et al. 2006).

Fig. 3. Summary of the signalling molecules released by cholangiocarcinoma-derived cancerassociated fibroblasts and their known effects on cholangiocarcinoma progression. CAFs; cancer-associated fibroblasts, HGF; hepatocyte growth factor, SDF-1; stromal derived factor-1.

One last cancer-associated fibroblast gene of note is the expression of the chemokine, stromal-derived factor 1, which is released from stromal fibroblasts and stimulates the invasion and migration of cholangiocarcinoma cells via interaction with the chemokine receptor, CXCR4 (Ohira et al. 2006). A summary of these and other cholangiocarcinomaderived cancer-associated fibroblasts can be found in Figure 3.

The preponderance of data demonstrating a role for cancer-associated fibroblasts in the growth and invasion of cholangiocarcinoma suggest that targeting molecular signals released from cancer-associated fibroblasts may be a viable option, in addition to strategies for suppressing cholangiocarcinoma cell proliferation, for the treatment of cholangiocarcinoma.
