An image worth a thousand lives?

An exciting array of novel antiproliferative systemic agents, including angiogenesis inhibitors, vascular targeting agents and signal transduction inhibitors have recently entered into clinical trials. With the exception of imatinib (Gleevec; Novartis, Basel), however, they have had lower than anticipated response rates. The quandary of whether the agent being investigated is actually interacting with its intended molecular target and whether the target is actually relevant to the growth drive for a given tumor is becoming even more acute as tremendous resources are expended for the potential benefit of fewer patients. In this issue, Smith-Jones et al. describe for the first time a positron emission tomography (PET) methodology that allows imaging of a molecular target in vivo over time.