P2.04-008 Diagnostic Performance of PET-CT for Anterior Mediastinal Lesions - The DECiMaL Study: Topic: Thymic Malignancies Clinical and Translational

Abstract

The diagnostic performance of 18-FDG positron emission tomography (PET) on the ability to differentiate malignant from benign lesions in the anterior mediastinum is not defined and therefore the clinical utility is unknown. The aim of this study is to collate multi-institutional data to determine the value by defining diagnostic performance of FDG PET/CT for malignancy in patients undergoing surgery with an anterior mediastinal mass. DECiMaL Study is a multicenter, retrospective, collaborative cohort study in seven UK sites. We included all patients undergoing surgery (diagnostic or therapeutic) who presented with an anterior mediastinal mass and underwent PET/CT as part of their diagnostic work-up. PET/CT was considered positive for any reported PET avidity as stated in the official report and the reference was the resected specimen reported by histopathology using WHO criteria. Diagnostic test performance was expressed as sensitivity, specificity, positive and negative predicted values with corresponding 95% confidence intervals. Between January 2002 and June 2015 a total of 134 patients were submitted with a mean age (SD) of 55 years (16) of which 69 (51%) were men. All patients had pre-operative PET CT and the histology was thymic hyperplasia in 10 patients (8%), thymic cyst in 8 (6%) and no malignancy in 15 (11%) and these were classified as “benign”. Histology was thymoma in 55 patients (41%), other malignancies in 38 (28%) and thymic carcinoma in 8 (6%), and these were classified as “malignant.” The sensitivity and specificity of PET/CT to correctly classify malignant disease were 83% (95% CI 74 to 89) and 58% (37 to 78). The positive and negative predictive values were 90% (83 to 95) and 42% (26 to 61%). The results of our study suggests reasonable sensitivity but no specificity implying that a negative PET/CT is useful to rule out the diagnosis of malignant disease whereas a positive result has no value in the discrimination between malignant and benign disease of the anterior mediastinum.