[The fluorescence: a "bright" concept for the study of the metastatic process].

The forming of secondary tumors, called metastases, constitutes the first cause of death of the patients reached by a cancer and represents one of the major obstacles in the fight against this disease. The characterization of mechanisms governing the passage of the cancerous phenotype into metastasis thus turns out to be a crucial stage for the discovery of new treatments. The understanding, and finally the inhibition of a so complex and multifactorial process, require the implementation of various strategies of study (e.g. inhibition of the neo-angiogenesis, impact of the expression or of the inhibition of a gene, test of a new molecule, etc.). However, whatever is the envisaged type of work, the use of in vivo models remains always essential. Unfortunately, although the classic approaches to show and count the metastases (histology, immunohistochemistry, etc.) allowed the better understanding of the metastatic process, these techniques dramatically underestimate the real number of metastases in a given tissue, because they do not allow the detection of the micrometastases. The aim of this article is to present a new approach in the models of studies of the metastases, using cancerous cells stably expressing the green fluorescent protein (GFP). The fluorescence emitted by the GFP, induced by UV radiation, allows to show up to the unicellular level the cancerous cells present to the healthy tissue of the host and so to estimate in a relative precise way their number. In addition, the power of detection of these models can be combined to video devices, allowing to follow the evolution of the tumor growth and the metastatic spread during time, and it on the same animal. These new models radically change the classic approaches of study of metastatic spread and open the way new types of works till now impracticable. In addition, besides the aptness of these models, we will also discuss their weaknesses, and will present some recent examples of applications.