Cells grown in 3D within natural extracellular matrices or synthetic scaffolds better recapitulate the phenotype of those cells within an organism in regard to normal developmental as well as pathobiological processes. 3D cultures also predict efficacy of, and resistance to, a wide variety of cancer therapies. We have used tissue-engineering approaches to establish 3D biomimetic avatars. We have shown that biomimetic avatars of human breast carcinomas [BCa] and human plexiform neurofibromas from patients with type 1 neurofibromatosis [NF1 PN] can be used to assess therapeutic efficacies of small molecule inhibitors of proteases and kinases, neutralizing or blocking antibodies to cytokines and photodynamic therapy. Conventional culture platforms do not support 3D culture of the large multi-cellular invasive structures formed by biomimetic avatars cultured over extended periods of time. Therefore, we have designed and fabricated modular engineered chambers for 3D culture that include microsensors for real-time (4D) non-invasive monitoring of pH and oxygen and that can be used for live-cell imaging of (patho)biological responses. We have demonstrated that BCa avatars will grow in our engineered chambers for as long as 70 days and can be imaged live over intervals during the entire time course. Many key parameters can be visualized in the biomimetic avatars, including spatio-temporal and dynamic interactions among the co-cultured cells and changes in proteolysis, morphometry, viability, proliferationand invasive phenotype. We predict that biomimetic avatars recapitulating cell:cell and cell:matrix interactions present in tissues in vivo will be useful for screening a wide variety of therapeutic approaches. Our ultimate goal is to develop biomimetic avatars from a patient’s tumor, avatars in which targeted “personalized medicine” therapies can be tested in in vitro N-of-1 clinical trials.