Ex Vivo Analysis of Primary Tumor Specimens for Evaluation of Cancer Therapeutics

The use of ex vivo drug sensitivity testing to predict drug activity in individual patients has been actively explored for almost 50 years without delivering a generally useful predictive capability. However, extended failure should not be an indicator of futility. This is especially true in cancer research, where ultimate success is often preceded by less successful attempts. For example, both immune-and genetic-based targeted therapies for cancer underwent numerous failed attempts before biological understanding, improved targets, and optimized drug development matured to facilitate an arsenal of transformational drugs. Similarly, directly assessing drug sensitivity of primary tumor biopsies and the use of this information to help direct therapeutic approaches has a long history with a definitive learningcurve. In this review, we survey the history of ex vivo testing and the current state of the art for this field. We present an update on methodologies and approaches, describe the use of these technologies to test cutting-edge drug classes, and describe an increasingly nuanced understanding of tumor types and models for which this strategy is most likely to succeed. We consider the relative strengths and weaknesses of predicting drug activity across the broad biological context of cancer patients and tumor types. This includes an analysis of the potential for ex vivo drug sensitivity testing to accurately predict drug activity within each of the biological hallmarks of cancer pathogenesis.