Angiogenèse et tumeurs du sein. L'apport du pathologiste

Angiogenesis is an essential step of the tumoral growth and of the metastatic dissemination. It provides the nutriments necessary to the tumor and by the direct contact of the lumen vessels, facilitates its metastatic extension. The activation implies a large number of different agents which closely interact with the extracellular matrix. The intra tumoral vessels constitute an irregular network with numerous shunts. Their wall is also abnormal, incompletely covered by pericytes, and their basal membrane is thin and fragmented, sometimes absent. These features are responsible for an increased permeability and despite the large number of vessels, deserve a less effective oxygenation. The hypoxia induced secondarily activates the synthesis of angiogenic factors. The pathologist receives today help from immunohistochemistry for the evaluation of angiogenesis. This means facilitates the detection of vessels by use of specific antibodies directed against the endothelial cells (CD31, CD34, fVIIIrag…). It also allows the quantification of vessels or “microvascular density”. Its importance varies from one patient to another and for different areas of a same tumour, the “hot-spot” generally located at its periphery. Despite its heterogeneity and the complexity of mechanisms involved in the regulation, the microvascular density appears to be an independent prognostic factor for tumour of different histological types. Immunohistochemistry also permits the evaluation of different characteristics of vessels and the tumour such as the activators (VEGF, FGF…) or their specific receptors (VEGF-R). Such analysis is also important for the determination of the prognosis but appears more interesting for the selection of the antiangiogenic treatment. However, this step will require the standardization of the immunohistochemistry techniques and the implementation of an external quality control.