Tumor metastatization is strictly dependent on the invasive capacity of neoplastic cells, and on the degree of vascularization of the tumor. Vascular invasion is usually detected on routinely stained histological sections, and is defined as the presence of tumor cells in lacunar spaces lined by endothelial-like cells. It is generally difficult to distinguish between tumor invasion of haematic versus lymphatic vessels. So far, attempts to increase the sensitivity of the method by immunostaining the sections for endothelial cell markers such as von Willebrand factor (vWF) and Ulex europeus, have not been completely rewarding, mainly because not all the vessels were effectively stained. The prognostic relevance of the degree of vascularization in a tumor was emphasized by Weidner et al. who showed that presence of "hot spot vascularization" in breast carcinoma and in other solid tumors is correlated with a worst prognosis. Some authors have confirmed these observations whereas others have not been able to find a significant correlation between tumor vascularization and prognosis.

In the recent past, we have used immunohistochemistry for investigating the tissue distribution of a new generation of endothelial cell markers including VE-cadherin and CD31 (J. Cell Biol. 118: 1511-1522, 1992). Furthermore, monoclonal antibodies to CD31, CD34 and VE-cadherin have been applied to the study of pathological conditions involving endothelial cells such as Kaposi's sarcoma (J. Pathol. 173: 23-31, 1994) and vascular tumors (J. Pathol. 175:51-57, 1995). In the present study we have investigated the reliability of these new reagents as endothelial cell markers for determining vascular invasion and tumor vascularization in solid tumors. We actively collaborate with other groups involved in endothelial cell biology. In these joint projects we provide the expertee for morphological studies on sections of normal and pathological tissues. In the context of these collaborations we will investigate the presence and the potential biological relevance in tumor angiogenesis of new molecules whose angiogenic activity has been previously established in vitro. The presence of the molecules will be investigated using immunohistochemistry and/or molecular biology techniques depending on the nature of the reagent available. In this last regard, our laboratory has the technology and the experience for RNA extraction from tissues, for detection of RNA transcripts by Northern blot analysis and by RT-PCR, and for in situ hybridization techniques on tissue sections.