68Ga-DOTATOC PET/CT in detecting neuroendocrine tumours responsible for initial or recurrent paraneoplastic Cushing's syndrome

Purpose Paraneoplastic Cushing's syndrome (PCS) is frequently caused by neuroendocrine tumours (NETs). Approximately 20% of tumours are still occult years later. Gallium-68 somatostatin receptor-PET/CT is promising for the detection of the causal primary NET, but its role in case of recurrent PCS is rarely reported. We report our experience with DOTATOC PET/CT in localising the causal NET in cases of initial but also recurrent PCS, and its clinical impact. Methods A retrospective review of all DOTATOC PET/CTs performed in consecutive patients referred for PCS to our centre, between January 2011 and June 2017, was done. Nineteen patients underwent 26 PET/CTs, 13 for detection of a primary NET, seven for persistent or recurrent PCS after resection, and six for surveillance after resection of NETs previously detected on a DOTATOC PET/CT in our centre. Results Among the 13 PET/CTs performed to search for primary NET, five were positive: four carcinoid lung tumours were confirmed after resection and one lung focus was not confirmed since surgery would have carried a high risk. Clinical impact was 23% (3/13). Among the seven PET/CTs performed for persistent or recurrent PCS, six were true-positive, with confirmation of metastatic lymph nodes after resection. Clinical impact was 57% (4/7). All PET/CTs performed for surveillance were true-negative. Conclusions DOTATOC PET/CT seems to be a valuable tool for detection of the NET responsible for persistent or recurrent PCS after surgery. In this context, DOTATOC PET/CT was more effective than for the detection of the causal tumour in initial PCS.