Animal Models for the Calculation of Circulating Tumor Cells for Experimental Demonstration

Metastasis is a process which is characterized by the existence of tumor cells in the bloodstream. This is a necessary situation in order for the malignant cells to be transported to other organs. Thus, the importance of circulating tumor cells (CTCs) in the study of carcinogenesis is widely accepted. These tumor cells are nowadays a topic of intensive research all over the world. CTCs are expressed from tumor cells and the clinical analysis of this expression may help the recognition of a tumor in an earlier stage and also there is an effort to monitor the tumor burden according to these cells. Although a plethora of clinical studies has been conducted, it is still unclear whether the use in clinical aspect will prove to be beneficial in the near future. Few animal models with neoplasia have been studied concerning the circulating tumor cells and it is likely that CTCs may have a predictive, diagnostic or therapeutic value. Herein, the authors review all studies in which human CTCs were transplanted into animals. Therefore, more clinical studies using standardized methods for measuring CTCs are required to elucidate these issues.