The overwhelming cause of morbidity in cancer patients is metastasis: the ability of tumor cells to mobilize, leave the primary tumor site, invad distant tissue, and launch secondary tumors. In 1889, Dr. Steven Paget analyzed data from hundreds of breast cancer fatalities and noted that metastases were most often found in a specific subset of organs, e.g. the bone, lung, brain, spleen, and liver. Prior to this study, it ws generally accepted that distant sites of metastasis were well-vascularized and had exceedingly narrow capillaries to physically trap circulating cells; however, Paget's findings can not be explained by vascularization alone, and the physicochemical traits of certain organs and tissues that make them predisposed for metastasis remain unknown. More recently, clinical studies have revealed that disease subtypes of breast cancer demonstrate differential spread patterns to brain, lung, and bone tissue. Reports are emerging that mesenchymal stem cells (MSCs) are present at the inflammatory tumor stroma, and that they may contribute to tumor to growth and in cancer cells acquiring metastatic traits. Similarly, my previous work has shown that MSC motility is sensitive to physicochemical matrix properties that vary in instances of inflammation. propose that, in addition to the primary site, the pre-metastatic niche is also an area of inflammation, and tissue specific stem cells (stem cells that reside in the local tissue and respond to injury) are activated by tumor released factors, and remodel the surrounding tissue, creating a favorable soil before the arrival of metastatic tumor cells. The goal of this proposal i to use engineered microenvironments to study this metastatic cascade of events: stem cell-tumor cell crosstalk, stem cell mobilization and ensuing remodeling of the pre-metastatic tissue, and the preferential attraction of circulating tumor cells to diverse tissue sites. Our engineered microenvironments are 3D, with orthogonal control of enzymatic degradation, integrin binding, and stiffness, and capture these physicochemical features of brain, lung, and bone tissue. We will quantify how tumor conditioned media regulates the ability of tissue specific stem cells to remodel these microenvironments, and whether this premetastatic niche formation is necessary to facilitate tissue tropism in breast cancer. Mechanistic approaches will test whether active proteolysis propels a positive feedback loop between matrix turnover and micrometastatic lesion formation. Completion of this proposal will catapult substantial progress in the field of cancer biology by revealing the physicochemical properties of materials and tissues that prime them for metastases, and by providing environments in which to study this and other biophysical mechanisms of cancer spread. My education and research training in Chemical Engineering, stem cell motility, and 3D tissue engineering has uniquely positioned me meet the challenges of this innovative research plan. !