Tumor heterogeneity is increasingly implicated in the limited therapeutic efficacy exerted by nanomedicines in vivo. Such heterogeneity is manifold - existing at macro- and microscopic scales, and subject to tumor differentiation, region, intervention, and time. Further, variable patient response to nano-based therapy has called into question the current pursuit, and practices, of nano-formulation development. Long-standing concepts in advanced drug delivery may therefore benefit from renewed examination in light of ongoing elucidations into tumor pathophysiology. Tumor microenvironmental features bear significant structural and functional constraints to effective nanomedicine delivery. Importantly, the relationship between delivery and therapeutic efficacy has proved elusive, owing to inefficient drug release from nanocarriers and/or target site access resulting from physical or physiological hindrance. Characterization of local tumor parameters as potential determinants of nanomedicine efficacy may complement conventional whole-tumor measurements. The challenges in identifying key determinants of nanomedicine efficacy and monitoring their impact in space and time are non-trivial. Newly developed image-based methodologies provide a non-invasive and quantitative means of measuring the performance of both nanomedicine (e.g., pharmacodynamic effect) and microenvironmental properties (e.g., abnormal supply and transport of nutrients/drugs), with the potential to enable appropriate treatment design. Ultimately, the personalization of anti-cancer therapies may require the characterization of underlying pathophysiological parameters, and their association with therapeutic outcomes. (C) 2016 Elsevier Ltd. All rights reserved.