Characterizing tumors using metabolic imaging: PET imaging of cellular proliferation and steroid receptors

Treatment decisions in oncology are increasingly guided by information on t he biologic characteristics of tumors. Currently, patient-specific informat ion on tumor biology is obtained from the analysis of biopsy material. Posi tron emission tomography (PET) provides quantitative estimates of regional biochemistry and receptor status and can overcome the sampling error and di fficulty in performing serial studies inherent with biopsy. Imaging using t he glucose metabolism tracer, 2-deoxy-2-fluoro-D-glucose (FDG), has demonst rated PET's ability to guide therapy in clinical oncology. In this review, we highlight PET approaches to imaging two other aspects of tumor biology: cellular proliferation and tumor steroid receptors. We review the biochemic al and biologic processes underlying the imaging, positron-emitting radioph armaceuticals that have been developed, quantitative image-analysis conside rations, and clinical studies to date. This provides a basis for evaluating future developments in these promising applications of PET metabolic imagi ng.