This proposal will establish patient-derived 3D co-cultured micro tumors that will be used both to screen anticancer therapeutic compounds in drug development, leading to fewer clinical trial failures because of earlier, more relevant results and to test patient-derived samples in real time for clinical decision making. Our initial strategy will be to establish a human relevant model of the breast cancer microenvironment which can be monitored and evaluated for response using non-destructive means. Initially, an existing bioengineered 3D mammary gland tissue models longevity, response to hormonal cues, and analytical evaluation improved through incorporation into a commercially available 3D co-culture perfusion system that permits non-destructive in situ monitoring. We will then characterize the effects of the diseased state (cancer) within the model by replacing the primary mammary epithelial cells with an immortalized, transformed breast cancer cell line using non-destructive analysis. Then, we will replace the immortalized cell lines with patient-derived primary breast epithelial tumor cells and treat with approved cancer drugs known to have clinical activity, in order to establish a benchmarked performance and proof of concept of the predictive power of the primary human 3D Co-cultures for drug development and real time therapeutic decision making.