The pre-metastatic niche: is metastasis random?

The metastasis of solid tumours is a vastly complex, dynamic and systemic process involving both primary tumour cells as well as a wide array of stromal and vascular cells. The recruitment and activation of host cells by tumours at both the primary and metastatic sites is crucial for successful metastatic dissemination highlighting the systemic nature of disease progression. The appropriation of distant metastatic sites by primary tumours and the generation of so-called pre-metastatic niches have gained much interest in the last decade complementing the century old 'seed and soil' hypothesis. The idea that tumours are capable of pre-defining future sites of metastasis is both exciting and terrifying as we try to understand the dynamic networks associated with solid tumour metastasis. Exactly how a tumour cell can alter the distant metastatic microenvironment is of great importance and will unlock novel strategies for successfully targeting these processes.