Cancer spread and micrometastasis development: Quantitative approaches for in vivo models

Death from cancer is usually due to metastasis. Fortunately, most cells that escape from a primary tumor fail to form metastases. Identifying reasons for this failure will help development of anti‐metastatic therapies. Intravital videomicroscopy (IVVM) can be used to observe cancer cells injected into live animals. Co‐injected microspheres can be used to assess cell survival. These techniques have been used to show that circulating tumor cells generally arrest in the microcirculation and may extravasate with high efficiency. While many tumor cells may survive in a secondary site, only a small subset form micrometastases and only a subset of these micrometastases persist to form vascularized macrometastases. Furthermore, solitary tumor cells may remain dormant for long periods of time in secondary sites. These findings suggest that metastatic growth and angiogenesis are prime targets for anti‐metastatic therapy. BioEssays 24:885–893, 2002. © 2002 Wiley Periodicals, Inc.