Lay Summary: PET should not be used to “fish” for a diagnosis. On the other hand, when a pathological diagnosis is already established, PET can be useful for follow-up, staging and reassessment after therapy.
PET scanning is an excellent modality to assess tumor size and metabolic activity and it is coming into wider use as supporting data becomes available for various tumor types. It can be used to distinguish benign and malignant tissues once a diagnosis has been made. Unfortunately, there is no literature to support use of PET to “fish” for diagnosis when no histologic diagnosis has been obtained. This is especially true of lymphadenopathy. Since lymphadenopathy can be caused by a variety of conditions with different degree of gadolinium uptake and different specificities, sensitivities and accuracies, PET is potentially misleading and even harmful when used in this fashion. A NCT00068146 study is looking at a related question: the usefulness of FDG-PET scanning in distinguishing autoimmune lymphoproliferative syndrome (ALPS) from lymphoma. Much more investigation will need to be done before PET can be used to distinguish different types of lymphadenopathies. While the use of PET is reasonable in some cancers when there is already a pathological diagnosis to distinguish benign from malignant disease sites or to evaluate a potential recurrence, it should not be used for this purpose before the diagnosis of malignancy had been established.
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