The metastatic niche: adapting the foreign soil

Abstract

How are sites of metastases chosen? Accumulating evidence suggests that primary tumour cells and circulating tumour cells might facilitate changes to the microenvironment in target organs so that a pre-metastatic niche, ideal for engraftment, forms. The 'seed and soil' hypothesis for metastasis sets forth the concept that a conducive microenvironment, or niche, is required for disseminating tumour cells to engraft distant sites. This Opinion presents emerging data that support this concept and outlines the potential mechanism and temporal sequence by which changes occur in tissues distant from the primary tumour. To enable improvements in the prognosis of advanced malignancy, early interventions that target both the disseminating seed and the metastatic soil are likely to be required.