Imaging as a pharmacodynamic and response biomarker in cancer

Imaging of biological and molecular processes has provided the platform for evaluating the hallmarks of cancer, such as metabolism, proliferation, tissue invasion, angiogenesis, apoptosis and hypoxia, and in turn for assessing the efficacy of treatments including novel targeted therapies. Cross-sectional imaging methods can measure response to chemotherapy and radiotherapy by measuring changes in tumour volume. Imaging modalities such as positron emission tomography and functional magnetic resonance imaging can non-invasively detect early molecular changes in response to therapy, provide guidance for therapy optimisation, and predict response to treatments and clinical outcome. In an era of escalating drug trial costs, with high attrition rates of early-phase studies, the development of an imaging biomarker can contribute to optimisation of proof of concept and patient stratification. In this review, we examine the current molecular imaging modalities used to assess pharmacodynamics and therapy response and highlight some novel emerging imaging strategies.