The focus of this project is to understand how nano-encapsulated formulations of common chemotherapies work in vivo by developing and utilizing intravital methods for studying drug and nanoparticle function in mouse breast cancer models. We hypothesize that, firstly, we can develop longitudinal breast cancer specific methods of imaging common chemotherapies and their nanoparticle equivalents. Secondly, we hypothesize that encapsulated drugs will be more effective in terms of specific cell responses as they achieve longer exposure times than unencapsulated drugs. Overall, this work will result in the creation of a breast cancer centered platform for drug development and analysis. At the clinical level, this study will result in pertinent data regarding several agents currently in clinical trials. At the basic science level, we will work to understand the heterogeneity of cell responses to drug treatments. Thus, we believe this project has potential impact in both the near and long term for breast cancer treatment.