The impact of (18)F-FDG-PET/CT on Merkel cell carcinoma management: a retrospective study of 66 scans from a single institution

Merkel cell carcinomas (MCC) are neuroendocrine skin tumours frequently responsible for lymph node recurrence and metastatic disease and for which optimal management remains to be defined. The objective of this study was to evaluate the impact of (18)F-fluorodeoxyglucose ((18)F-FDG)-PET/computed tomography (CT) on the staging and treatment of MCC patients. Twenty-three patients with a histologic diagnosis of MCC explored by (18)F-FDG-PET/CT between 2004 and 2012 were retrospectively included in the study. The detection of new lesions and the change in tumour staging and treatment were evaluated. For each patient, the (18)F-FDG-PET/CT results were compared with histological, clinical and imaging data. Sixty-six (18)F-FDG-PET/CT scans were performed at initial presentation (n=18), during subsequent monitoring (n=34) or during evaluation of chemotherapy response (n=14). The sensitivity, specificity and positive and negative predictive values of the (18)F-FDG-PET/CT were 97, 89, 94 and 94%, respectively. Two false-positive results (lymphadenitis) and one false-negative result (regional metastatic lymph nodes) were accounted for. Lesions not detected clinically or by conventional imaging techniques were found in 44% of the 52 (18)F-FDG-PET/CTs performed at initial presentation and subsequent monitoring, with, respectively, 50 and 41% of scans identifying new lesions. At initial presentation, (18)F-FDG-PET/CT led to a change in tumour staging in 39% of patients. Patient management was modified by (18)F-FDG-PET/CT results in one-third of patients (33% of patients at initial presentation, 32% during subsequent monitoring and 36% during evaluation of chemotherapy response). F-FDG-PET/CT incidentally detected four additional histologically confirmed cancers. This retrospective study confirms the important impact of (18)F-FDG-PET/CT on the management of MCC patients.