It is important to note that the metastatic cells do not float about in isolation; rather, they reside within the extra-cellular matrix (ECM) of the host organ. The ECM is a complex mesh of proteins that fill voids be- tween cells, and it participates in the development of both healthy and cancer cells through chemical and mechanical signalling. There is evidence that changes in the stiffness of the ECM affect the signalling and hence the progress of the cancer. In turn, it seems that the cancer cells can interact with the ECM to trigger the very physical changes that favour the tumour’s development. Thus, in effect, metastatic cells create a “nest”.
