**3.1.1 Relevance of cytokines in HCC circulating tumor cells**

Hepatocellular carcinoma tumor has shown to secret a lot of cytokines related to the development of the tumor, like vascular endothelial growth factor (VEGF), transforming growth factor-beta 1 (TGF-β1), Interleukin 8 (IL-8) or tumor-specific growth factor (TSGF). These serum markers are useful to follow-up the development and the prognosis of the HCC but useless to follow-up circulating tumor cells in blood (Zhou et al., 2006).
