Interest of (18)F-FDG PET-CT scanning for staging and management of merkel cell carcinoma: a retrospective study of 15 patients

Background The additional benefit of 18FDG-Positron Emission Tomography-Computed Tomography (FDG PET-CT) compared with conventional imaging is still a controversial issue in MCC. Objectives This study was designed to evaluate the ability of FDG PET-CT to detect secondary lesions clinically inconspicuous and not shown by conventional imaging. Methods Clinical records of 15 MCC patients were retrospectively reviewed to investigate the specific interest of FDG PET-CT compared with X-computed tomography (CT). The main endpoint was the ability of FDG PET-CT to detect secondary lesions and the possible resulting changes in disease staging and management compared with pre-FDG PET-CT data including clinical examination, sentinel lymph node biopsy (SLNB), and diagnostic CT. Results FDG PET-CT was relevant with a single false negative result and led to significant changes in disease staging and management in 46% of patients compared with clinical examination alone. However, additional secondary lesions not detected by CT were evidenced during follow-up in a single patient with an already known metastatic disease, data which did not result in any change in staging and treatment. Sensitivity, specificity, positive predictive value and negative predictive value were respectively 0.66, 1, 1 and 0.8 for SLNB, 0.89, 1, 1 and 0.93 for CT and 0.89, 1, 1 and 0.93 for FDG PET-CT. No additional neoplasm was detected by FDG PET-CT. Conclusion Although FDG PET-CT is of questionable value in MCC management when used in parallel with CT, it may be considered as a valuable option as a single whole-body survey procedure.