Somatostatin receptor positron emission tomography/computed tomography imaging in Merkel cell carcinoma

Background Merkel cell carcinoma ( MCC ) is an uncommon aggressive primary cutaneous carcinoma with neuroendocrine differentiation. However, literature data about the use of somatostatin receptor positron emission tomography/computed tomography ( PET / CT ) imaging in MCC are limited and its role is not clearly stated. Objective To investigate the role of PET / CT using somatostatin analogues radiolabelled with gallium‐68 in patients with MCC . Methods All patients affected by MCC who performed a somatostatin receptor PET / CT imaging from October 2007 to May 2014 were retrospectively analysed. The diagnostic performances of PET / CT were evaluated on a patient‐based analysis and compared to final diagnosis (histology = 3 or clinical/radiological follow‐up = 20). Results We evaluated 23 consecutive MCC patients [18 men; median age 71 years (range 47–87)]. Primary tumour was located in ear (1/23), cheek (3/23), arm (2/23), hand (1/23), back (1/23), anal canal (1/23), gluteus (4/23), thigh (3/23) and popliteal fossa (1/23). In 6/23 patients, the site of primary tumour was unknown. PET / CT was performed to detect primary tumour site (4/23) or to stage (8/23) or re‐stage (11/23) patients. PET / CT resulted positive in 14/23 patients and according to the final diagnosis was defined true positive, true negative, false positive ( FP ) and false negative in 11/23, 8/23, 3/23 and 1/23 cases respectively. FP PET / CT results were due to unspecific liver uptake, post‐surgical inflammation and pancreatic neuroendocrine tumour. PET / CT was unable to detect primary tumour site in all patients with unknown primary MCC . Sensitivity, specificity and diagnostic accuracy of PET / CT were 92%, 73% and 83% respectively. Conclusions In our experience, somatostatin receptor PET / CT imaging resulted useful in patients with MCC and presented high diagnostic performances with a significant impact in disease management although in patients with unknown primary MCC , it was unable to identify the primary tumour site.