**4.2.2 Culture of CTC**

After isolation of the CTC by the different methods described above, to increase the number of CTC, the primary tumor cells can be cultured in the specific culture medium (Allard et al., 2004). The optimal conditions of culture growth and specially the culture medium leading the growth of the CTC, but not the other epithelial or non epithelial cells, have to be determined through an experiment. Some companies propose commercial kits. For example, The Cancer Cell Isolation Kit® from Panomics includes lysis buffer to increase the number of CTC. One of the main problems is that cultured cells can lose their original markers and derive. Mimicry of tumoral microenvironment *in vitro* is particularly difficult because for most tumors it is largely unknown. Another problem is that the samples containing the CTC are usually contaminated by stromal cells like fibroblasts, which create competition in the Petri dish. After few days, only the fibroblasts are present in the flask.
