Surgery (RMH) - Theses
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ItemManagement of PET-avid thyroid nodules in cancer patients( 2017)Background and aims: FDG-avid thyroid incidentalomas (TI) are common findings (2.5%) in patients imaged for staging or treatment response and represent thyroid cancer in approximately 35% of cases. Consequently, the 2015 ATA guidelines strongly recommend investigation of such nodules ≥1cm without considering the prognosis of underlying malignancy. In addition, the utility of SUV-max which observes maximum uptake of FDG also has been the described as a potential surrogate marker of thyroid cancer. This study aims to assess the overall and thyroid cancer specific survival in a large cohort of FDG-avid TI; assess the role of SUV-max in predicting thyroid cancer in this cohort; and observe potential confounders of highly avid thyroid nodules – notably benign Hürthle cell adenomas. Methods: A retrospective review was performed on all patients at Peter MacCallum Cancer Centre between 2007 and 2015. 45, 680 consecutive PET/CT scan reports were reviewed, identifying 2588 reports referring to the thyroid. Scan duplicates and normal thyroid reports were excluded. Other exclusions included physiological uptake to the thyroid gland, thyroiditis, patients known thyroid cancer, multi-nodular goitre, focal uptake less than 1mm and nodules identified with non-FDG radiotracers. FDG-avidity parameter data was gathered using MIM imaging software. Variables including age, gender, follow-up time >12 months, primary malignancy, overall survival, thyroid cancer-specific survival, cytology and histopathology were collected until January 2016. Multivariate logistic regression, survival analysis and receiver operator curve (ROC) analysis was performed. Results: The study included 362 patients who met the inclusion criteria with median age 65 years (range 19-96), and median follow-up of 24 months (range 1-103). Lymphoid, lung and colorectal malignancy were the most common indications for staging. The median overall survival was 20 months (IQR 9.5-39). The majority of deaths was due to the primary malignancy (92.2%). One patient (0.6%) died from incidental medullary thyroid cancer. FDG-avidity in primary malignancy, advanced stage and clinician decision to not investigate FDG-avid TI were all predictors of mortality with hazard ratios of 8.5 (95%CI 4.6-15.8), 3.0 (95%CI 2.3-3.9) and 3.3 (95%CI 2.0-5.0) respectively (P<0.001). Receiver operator curve (ROC) analysis demonstrated on optimal SUV-max threshold of 5.33. Sensitivity and specificity of thyroid cancer detected incidentally on PET/CT on ROC analysis was 73.47 and 46.94 respectively, with a broad area under the ROC curve of 0.66 (p = 0.005). Five nodules (20%) necessitated revision of diagnosis on correlative histopathologic-imaging review. Two presumed malignant FDG-avid TI found on imaging were correlated to non-malignant Hürthle cell adenomas on pathology, indicating misclassification by location. Conclusion: The overall survival with FDG-avid TI was poor due to the prognosis associated with underlying malignancy which must be considered prior to investigation of FDG-avid TI. Active surveillance should be considered in this group of patients. SUV-max is not a safe tool to discriminate benign from malignant TI and should remain a theoretical adjunctive tool for predicting thyroid cancer. Benign and malignant oncocytic lesions are a common cause of FDG-avid TI. The incidence of FDG-avid malignancy may be overestimated without careful imaging and histopathologic correlation.