Tumor Cell Intravasation Alu-cidated The Chick Embryo Opens the Window

Tumor Cell Intravasation Minireview Alu-cidated: The Chick Embryo Opens the Window level, it is a dramatic breach of the normal situation of organizational stability of tissues. However, it should be noted that vascular dissemination is utilized to a limited extent during normal embryogenesis for the correct positioning of cells arising in one location and whose final location is in a distant tissue. Vascular transport of the Davis, California 95616-8535 primordial germ cells, arguably the most important cell type of the body, is a dramatic example of this process in the developing embryo. In the adult, lymphocytes and In the normal situation, the organization of the tissues leucocytes intravasate from their tissues of origin to and organs is stable for the life of the organism. The circulate in the blood and then extravasate at sites of dissemination of cells from a primary tumor by invasion inflammation. Thus, a full understanding of the mecha-and metastasis represents the best-known situation nisms of tissue metastasis is both of major fundamental where the normal restraints stabilizing cellular position-and applied interest. ing in the tissues are in abeyance (Armstrong, 1984). What are the cellular and molecular processes utilized Invasion is the intrusion of cells of one tissue type into by the tumor to establish colonies in distant tissues? the fabric of contiguous tissues and is responsible for Interestingly, we now know a great deal about the first the local dissemination of neoplastic tissue. Metastasis step of metastasis, tumor angiogenesis (Hanahan and is the dissemination of tumor cells to organs distant from the parent tumor and involves the transport of single cells or small clusters of neoplastic cells through the fluid spaces of the body. The avenues for metastasis include the cerebrospinal fluid, the peritoneal fluid, the lymph, and the blood. The most frequent route for tumor metastasis utilizes the vasculature, and vascular metas-tasis has received the most study from experimentalists. As the hallmark of tumor malignancy, the processes responsible for tumor dissemination have come under increasing scrutiny in recent years. Metastasis of solid tumors is a complicated multistep cascade that is initiated in most cases by the invasion of the tumor by capillaries from the surrounding host tissues. Tumor vascularization clearly is one of the rate-limiting steps for tumor growth and metastasis, because unvascu-larized primary tumors typically are maintained as small dormant nodules of tissue whose volume is kept constant by a balance of cell proliferation …