Tumor-stroma: In vivo assays and intravital imaging to study cell migration and metastasis.

The development of metastatic disease is often correlated with poor patient outcome in a variety of different cancers. The metastatic cascade is a complex, multistep process that involves the growth of the primary tumor and angiogenesis, invasion into the local environment, intravasation into the vasculature, tumor cell survival in the circulation, extravasation from the vasculature and sustained growth at secondary organ sites to form metastases. Although in vitro assays of single cell types can provide information regarding cell autonomous mechanisms contributing to metastasis, the in vivo microenvironment entails a network of interactions between cells which is also important. Insight into the mechanisms underlying tumor cell migration, invasion and metastasis in vivo has been aided by development of multiphoton microscopy and in vivo assays, which we will review here.