Circulating tumor cells and host immunity: A tricky liaison

During their dissemination, circulating tumor cells (CTCs) steadily face the immune system, which is a key player in the whole metastatic cascade, from intravasation to the CTC colonization of distant sites. In this chapter, we will go through the description of immune cells involved in this controversial dialogue encompassing both the anti-tumor activity and the tumor-promoting and immunosuppressive function mediated by several circulating immune effectors as natural killer (NK) cells, CD4(+) and CD8(+) T lymphocytes, T helper 17, regulatory T cells, neutrophils, monocytes, macrophages, myeloid-derived suppressor cells, dendritic cells, and platelets. Then, we will report on the same interaction from the CTCs point of view, depicting the direct and indirect mechanisms of crosstalk with the above mentioned immune cells. Finally, we will report the recent literature evidence on the potential prognostic role of the integrated CTCs and immune cells monitoring in cancer patients management.