The role of the microenvironment in tumor progression is an emerging area of research that clearly has important clinical implications, both for diagnosis and treatment of human carcinoma. The conversion of normal epithelial cells to metastatic tumor cells is accepted as a multi-stage process that requires progressive genetic alterations within the epithelial tumor cell and has been the focus of intense investigation. However, the many other cell types in the tumor microenvironment are increasingly appreciated as components of a complex biological network, akin to an organ system, that are critical for tumor progression. The members of this Program Project Grant will use both human genetic approaches and mouse genetic models to study gene action from two cell types in the tumor microenvironment: tumor stromal fibroblasts and macrophages. The program consists of three interactive Projects supported by four Cores. Project 1 will use human genetic approaches and laser capture microdissection to analyze genetic alterations that occur in the stromal compartment of human breast cancer samples. Projects 1, 2 and 3 will develop and use mouse models to experimentally test the role of three genetic pathways: Pten, Rb/E2F and ras/ets-2 in the tumor microenvironment. This work will be supported by the Transgenic/Knockout Core, the Mouse Pathology Core, the Research Methods and Biostatistics Core and the Administrative Core. The major, immediate goals of this program are: 1) identification on a genome-wide scale of genetic alterations that occur in mammary tumor stromal cells isolated from human mammary tumor samples and the correlation of genetic changes found in mammary tumor stroma with clinical outcome of breast cancer patients; 2) experimental verification of the essential role of gene action from mammary stromal cells during mammary tumor progression. This involves creation of mouse models that allow gene action in cells of the microenvironment to be tested and that should more accurately reflect mammary tumor progression in humans at the genetic level. The long-term goal of this Program is to use the information gained from our increased understanding of the role of the tumor microenvironment in breast cancer progress to improve strategies for the diagnosis, prognostication and treatment of human breast cancer.