Fluorodeoxyglucose positron emission tomography/computerized tomography in differentiated thyroid cancer management: Importance of clinical justification and value in predicting survival

The purpose of this study was to evaluate the added value of follow‐up fluorodeoxyglucose positron emission tomography/computed tomography ( FDG PET / CT ) to clinical assessment and predicting survival outcome in patients with differentiated thyroid cancers. Methods This is an institutional review board approved, retrospective study of 202 biopsy‐proven thyroid cancer patients at a single tertiary centre. A total of 327 follow‐up or surveillance PET / CT scans done 6 or more months from initial treatment completion were included in this study. Median follow‐up from completion of primary treatment was 94 months (range, 6.17–534.1 months). Overall survival benefit was measured using K aplan– M eier plots with a M antel– C ox log‐rank test. Multivariate C ox regression model is provided with clinical covariates. Results Of the 327 PET / CT scans from 202 patients, 161 were positive and 166 as negative for recurrence or metastasis. A total of 23 patients died during the study period. Patients with a positive PET / CT scan had shorter overall survival than those who had a negative scan ( P  < 0.0001, hazard ratio 6.1 (3.0–14.3) ). In the context of clinical assessment, PET / CT identified recurrence in 50% (25/50) of scans without prior clinical suspicion and ruled out recurrence in 36.8% (102/277) of scans with prior clinical suspicion. In a multivariate C ox regression model, factors associated with overall survival were stage ( P  < 0.0001), time to scan ( P  = 0.0005) and PET / CT result ( P  < 0.0001). Conclusion FDG PET / CT performed in follow‐up more than 6 months from primary treatment completion adds value to clinical judgment and a prognostic marker of overall survival in thyroid cancer patients.