The Clinical Impact of [⁶⁸Ga]-DOTATATE PET/CT for the Diagnosis and Management of Ectopic Adrenocorticotropic Hormone – Secreting Tumours

Objectives: Localization of ectopic ACTH-secreting tumours causing Cushing syndrome (ECS) is essential for clinical management, yet often difficult. [⁶⁸Ga]-DOTATATE PET/CT ([⁶⁸Ga]-DOTA-(Tyr³)-octreotate)] is an FDA-approved high-resolution diagnostic tool for imaging neuroendocrine tumours. Data on the clinical utility of [⁶⁸Ga]-DOTATATE in patients with ECS, however, are scarce. The objectives of this study were to determine the efficacy for ECS localization and the clinical benefit of [⁶⁸Ga]-DOTATATE imaging. Method: We conducted a retrospective review of all cases with ECS evaluated with [⁶⁸Ga]-DOTATATE from November 2016 through October 2018 at three referral centres. The clinical benefit of [⁶⁸Ga]-DOTATATE was based on detection of new tumours and resultant changes in management. Results: Over the study period, 28 patients with ECS underwent [⁶⁸Ga]-DOTATATE: 17 for identification of the primary tumour and 11 during follow-up. [⁶⁸Ga]-DOTATATE identified the suspected primary ECS in 11/17 patients (65%). Of these, nine patients underwent surgery: eight with confirmed ECS (5 bronchial, 1 thymic, 1 pancreatic and 1 metastatic neuroendocrine tumour of unknown primary origin) and one patient with a false-positive scan (adrenal gland). Of the 11 patients with ECS who underwent [⁶⁸Ga]-DOTATATE evaluation during follow-up, the study led to changes in clinical management in 7/11 (64%) patients. Conclusions: [⁶⁸Ga]-DOTATATE is sensitive in detecting primary and metastatic ECS, often identifies occult tumours after conventional imaging, and impacts clinical care in the majority of patients.