The role of FDG PET/CT in clinical evaluation and management of nasopharyngeal carcinoma

Introduction: To provide a broad overview of the evolving role of FDG PET/CT in clinical management of nasopharyngeal carcinoma and convey recent findings pertaining to FDG PET/CT’s advantages of guiding patient care and predicting patient prognosis.

Methods: Large scientific databases, including Google Scholar, PubMed, and Web of Science, were used to accumulate review articles and case reports that involved FDG-PET as a primary imaging modality used to assess treatment of nasopharyngeal carcinoma. This review will encompass today’s knowledge of head and neck disorders as derived from FDG-PET studies, and a large subset of such studies will reflect the most recent innovations regarding the use of FDG-PET molecular imaging of nasopharyngeal carcinoma.

Results: 18F-fluoro-deoxyglucose (FDG) is the most frequently used radiotracer in clinical practice. FDG is a useful marker for metabolically active cells, such as cancer and inflammatory cells, which use glucose as an energy source for their metabolic needs.

Several studies have displayed the vast utility of FDG-PET/CT in helping clinicians manage a wide array of pathologies, including malignancy of the head and neck such as nasopharyngeal carcinoma and squamous cell carcinoma. PET/CT provides both molecular and anatomical information, and superior to other imaging modalities in detecting primary tumors and distant metastasis because of its high positive and negative predictive values. FDG PET/CT’s high negative predictive value is useful in post-treatment surveillance of nasopharyngeal carcinoma as it can help predict risk of nasopharyngeal carcinoma recurrence and avoid unnecessary, cumbersome diagnostic sampling of patients in remission.

Imaging used concurrently with other biomarkers can help clinicians generate the most optimal patient-centered management strategy. For example, FDG-PET/CT can be used concurrently with Ebstein Barr Virus (EBV) DNA titers to analyze treatment responses and classify subgroups that have different survival rates. Studies have reported that patients with total lesion glycolysis (TLG) ratios below 0.6 with positive EBV DNA titres are more likely to have unfavorable outcomes (TLG reduction ratio is equal to the difference between TLG reduction pre and post treatment divided by the value of pre-treatment TLG). A lower TLG reduction ratio has been reported as a predictor of low response to therapy and worsened mortality risk. FDG PET/CT may also identify presence of recurrent or persistent post-chemotherapy malignancies and is very useful in nasopharyngeal carcinoma tumor staging. FDG PET/CT has also shown its utility when guiding clinicians to and avoid unnecessary aggressive locoregional chemotherapy and instead treat malignancies that have metastasized to distal sites. Earlier detection and intervention of metastatic malignancies can potentially improve nasopharyngeal carcinoma patient outcomes.

Conclusions: Many studies have looked at the impact of FDG-PET/CT on tumor staging, however, there is still more future work to be done to fully characterize the use of FDG-PET/CT in nasopharyngeal carcinoma. FDG-PET/CT can be used in combination with known prognostic and/or diagnostic biomarkers to evaluate how treatment efficacy in nasopharyngeal carcinoma. Some recent studies have suggested use of PET parameters like TLG reduction ratios to validly evaluate progression of nasopharyngeal carcinoma. A reduced TLG reduction ratio has been proposed to be a predictor for worse patient outcomes and indicate which patients require earlier medical intervention, however, there is no clear consensus and further investigation is warranted. Although there is a respectable amount of retrospective literature pertaining to FDG-PET/CT use to improve clinical management and diagnosis of nasopharyngeal carcinoma, there is a need for more current, prospective studies evaluating the critical, useful information elucidated by FDG-PET/CT in the constantly evolving field of medical oncology.