Biochemical and physical perturbations in tumor environments, cell signaling pathways, and transcriptional outputs intersect to control functional heterogeneity of cancer cells. Heterogeneity exists among populations of cancer cells under different environmental conditions and single cancer cells even in seemingly identical environments. Discovering mechanisms driving tumor heterogeneity and its impact on tumor initiation, metastasis, and response to therapy are essential to success of precision medicine. As an expert in molecular imaging, cancer model systems, and cancer biology, my challenge is to develop approaches to quantify key processes in cancer biology, including signaling and metabolism, in complex living systems. My expertise in fluorescence and bioluminescence imaging make me uniquely qualified to meet this challenge. I am a pioneer of in vivo bioluminescence imaging of biochemical events, having invented firefly luciferase complementation. I remain at the forefront of developing new bioluminescence methods for discovery in cancer. I have a strong record of engineering new reporters and implementing methods to extend capabilities of in vivo multiphoton microscopy, both with multi-plexed imaging reporters and fluorescence lifetime imaging. To capture tumor heterogeneity from imaging data, I write custom image processing code to automatically segment and quantify multiple imaging reporter signals from thousands of cells. My effort is fully funded by 3 NCI research programs. 1) Systems Bioengineering of Cancer Cell Migration: Discover mechanisms of gradient formation driving cancer cell migration through a combination of tissue engineered environments, mouse tumors, and computational models; 2) Environmental Regulation of Cancer Stem Cell Plasticity in Metastasis: Establish how physical components of tumor environments regulate breast cancer stem cells in primary and metastatic sites; and 3) Wireless Implantable Electronic Biosensors for Tumor Monitoring: Engineer mm-scale implantable biosensors to monitor tumors and detect early response to therapy based on environmental conditions such as interstitial pressure and pH. These projects are dynamic, productive multidisciplinary collaborations among myself, the Research Director, Dr. Gary Luker, MD, and a network of excellent investigators in breast oncology and chemical, biomedical and electrical engineering. My multidisciplinary expertise and experience allow me to effectively bridge the gap that may exist between scientists from disparate disciplines of biology and engineering. This award will enable me to continue interdisciplinary molecular imaging research focused on understanding and overcoming tumor heterogeneity to advance precision medicine in breast cancer.