Inflammatory breast cancer (IBC), which involves diffuse tumor cells migrating throughout the breast instead of a mass, skin invasion, and treatment resistance, is rare but accounts for approximately 10% of breast cancer mortality. Despite the name, these clinical signs are caused by blockage of lymphatic channels and skin invasion, not by classic inflammation. Unfortunately, most IBC xenograft models fail to re-capitulate the clinical phenotype of skin invasion and diffuse local spread, a significant limitatin to understanding IBC. In addition, numerous patient tissue studies comparing IBC and non-IBC tumor cells have failed to identify robust genomic or expression differences that drive this unique presentation. Interestingly, our preliminary studies of non-tumor breast tissue > 5cm from tumor in IBC and non-IBC patients (i.e., normal adjacent tissue, the "field") have identified significant differences in macrophage infiltration (increased) and breast stem cell distribution (dispersed) in IBC normal breast tissue. Importantly, in two cases for which pre-malignancy biopsies were available, these differences were demonstrated 10 years prior to diagnosis, suggesting altered homeostasis throughout the breast tissue prior to developing cancer. Further, we recently demonstrated that co-injection of IBC tumor cells with mesenchymal stromal cells (MSCs) induced diffuse skin invasion in IBC xenografts. On the basis of findings in apparently normal breast tissue adjacent to IBC tumors, we hypothesize that epidemiology factors including breast feeding and obesity stimulate macrophage, mesenchymal stem cell and breast stem cell (MMS) interactions prior to the initiation of a cancer, and that these interaction create a field effect that ultimately mediates the IBC phenotype. We propose, using organotypic co-cultures, a novel MSC/IBC xenograft that recapitulates the IBC phenotype, and an innovative, erasable multiplexing, hyperspectral immunofluorescence technology, to characterize MMS interactions in IBC in vitro, to determine if these interactions are necessary for the IBC phenotype in mice, and to image these interactions and related signaling in normal breast tissues from IBC patients. This work is significant because IBC, although rare, accounts for 10% of breast cancer deaths. With co- injection of MSCs in IBC animal models, for the first time, MMS interactions can be manipulated in an animal model to evaluate the clinical hallmarks of IBC. We propose to apply a novel imaging strategy to demonstrate these interactions in IBC normal adjacent tissues from patient samples and animal models, representing a highly innovative, translational approach to visualize niches not possible with standard techniques. Identification of the mediator of the IBC phenotype as being pre-malignant change would dramatically impact therapeutic design strategies for this disease and would potentially influence screening and early detection.