Breast tumors are surrounded by and in contact with by many types of non-cancer cells including fibroblasts and blood cells. These surrounding normal cells are collectively termed the “tumor microenvironment”, and the interplay between tumor cells with these nearby non-tumor cells may greatly affect all steps of cancer progression. The Ostrowski lab has shown that certain genetic changes in the fibroblasts that surround a breast tumor greatly accelerates mammary tumor formation in mouse models of breast cancer. These studies emphasize the importance of the tumor microenvironment in breast carcinogenesis, and more importantly, suggest that to develop more effective treatments against breast cancer we must target not only the tumor cells themselves, but also the cells of the tumor microenvironment. My research focuses on novel factors in the breast tumor microenvironment and in the breast cancer metastatic microenvironment that we predict could be utilized as therapeutic targets.