The glucose analogue fluorodeoxyglucose (FDG) has demonstrated enhanced uptake in the majority of tumours as a result of increased uptake and fixation by phosphorylation. It is the most widely used radiotracer in positron emission tomography (PET), being used in >90% of scans, and is useful for diagnosis, staging and detection of residual/recurrent cancer. However, there are limits to the utility of FDG, particularly in certain tumour types. The development of new radiotracers to study molecular processes such as proliferation, apoptosis, angiogenesis and hypoxia will complement FDG by providing additional information on the cell biology of tumours. The aim of this paper is to consider how the availability of new tracers, or new applications for existing PET/CT technologies, could deliver clinical benefit in cancer, using breast cancer as a paradigm.