Measuring Tumor Metabolism by 18F-FDG PET Predicts Outcome in a Multicenter Study: A Step Off in the Right Direction

As a widely used diagnostic tool, 18F-FDG PET/CT combines anatomic imaging with functional imaging and provides qualitative and quantitative information about tumor metabolic activity by as-signing a standardized uptake value (SUV) measurement of the relative uptake of 18F-FDG in a given tumor. 18F-FDG PET can serve as a prognostic marker (1–3) and is routinely used for di-agnostic staging, for recurrence evaluation, and to assess response to therapy or disease progression in multiple malignancies including breast cancer (4,5). Notably, because of its high sensitivity in the detection of therapy-induced glucose metabolic rate changes that may not be evident in anatomic images, particularly early after treatment, 18F-FDG PET has held promise as a biomarker of early response for decades (6–8). In this regard, 18F-FDG PET can serve as an integral marker that allows for a response-adapted therapeutic strategy wherein identification of sensitive or resistant tumors as early as a few weeks after treatment initiation allows patients to avoid toxic and futile therapies and directs patients toward an ag-gressive or investigational approach in an effort to maximize their outcome (9). This strategy has certainly proven practice-changing for patients with non-Hodgkin lymphoma (3). See page 31 In breast cancer, the neoadjuvant setting has been recognized as ideal for evaluating surrogate biomarkers for the prediction of pathologic complete response (pCR) to therapy and clinical out-come. In this context, 18F-FDG PET has certainly served as a suc-cessful integrated marker—that is, a marker used to compare the efficacy of different treatments but not for directing change in ther-apy in a prospective setting (9,10). Although using PET to identify responding patients has been of interest, in some tumors, responding patients continue to derive further benefit from therapy, and tumors that are progressive on first-line therapy frequently continue to progress even with salvage or experimental regimens. Nevertheless, subjecting patients to futile therapy when resection or other novel promising therapies are available seems truly inappropriate. Hence, we read with interest the collaborative efforts of Connolly et al