A fatal affair: Circulating tumor cell relationships that shape metastasis

Circulating tumor cells are metastatic precursors in several cancer types. Their biology and clinical utility are subject to numerous investigations, yet one aspect that is often neglected is their entanglement with the tumor microenvironment, namely the cross talk with stromal and immune cells and their relationships with other tumor-derived components such as circulating tumor DNA and extracellular vesicles in circulation. We will focus our short review specifically on these aspects, i.e., providing some examples of the liaison that circulating tumor cells have with stromal or immune cells and illustrating their relationship with other circulating tumor derivatives such as circulating tumor DNA and extracellular vesicles.