PET Diagnosis and Response Monitoring in Oncology

Positron emission tomography (PET) imaging plays many critical roles in the management of cancer patients including at diagnosis, staging, and in restaging after therapy. PET is also playing a critical role in assessing the response of cancers to therapy, early in their treatment. Most PET is now done as PET/CT although some use of PET/MRI in specific parts of the body is also performed. Most PET imaging is performed using the glucose analog fluorodeoxyglucose (FDG), which traces the increased rates of metabolism present in most cancers. At diagnosis, PET can help determine whether a biopsy is necessary and what location to biopsy. For staging, the precise location of the tumor dictates the choice and extent of surgery and can help define-and redefine-radiation therapy fields. For restaging, PET can help determine if any viable tumor remains after completion of therapy, thus defining whether additional treatment is necessary. Intratherapy monitoring can be used to help define excellent and poor responders, potentially leading to deescalation of therapeutic intensity or to intensification, even including stem cell transplant approaches. Although FDG is widely used, other niche PET tracers are important including those that target somatostatin receptors, prostate-specific membrane antigen, amino acid transport and metabolism, estrogen receptors, proliferation, bone turnover, and additional processes. Thus, quantitative noninvasive phenotyping is feasible using oncologic PET, and these approaches are critically important in guiding cancer therapies. More tracers are expected to emerge allowing PET to guide precision cancer therapies.