Imaging in the Age of Molecular Medicine: Monitoring of Anti-Angiogenic Treatments

Angiogenesis is a complex multistep process and a crucial pre-requisite for tumor growth, invasion and metastasis. A profound knowledge of the mechanisms including the elucidation of markers for angiogenic vessels is essential for the generation of new anti-angiogenic chemotherapeutic agents and the improvement of specific imaging techniques. During the last decades, numerous angiogenesis inhibitors have been developed and some of them have shown promising results in preclinical and clinical trials. However, the response to anti-angiogenic treatment is often delayed and shows high inter-individual variations. In order to improve anti-angiogenic therapy, new specific surrogate markers are necessary that allow the characterization of different angiogenic steps, especially at the early stage. In this respect, non-invasive imaging is a potent tool for characterizing the tumor vascularization and for sensitive and longitudinal treatment monitoring. In particular, new molecular imaging techniques might ultimately improve the characterization of the angiogenic tumor phenotype and stage. This review summarizes the current status of different imaging modalities e.g. MRI, CT, US, nuclear and optical imaging with respect to the imaging of tumor angiogenesis and of anti-angiogenic treatments. It also includes new approaches in molecular imaging, which give deep insight into the tumor stage and the response of tumor vessels to anti-angiogenic therapy. Thus, this may lead to a more personalized cancer therapy in future.