Lack of clinical impact of 18F-fluorodeoxyglucose positron emission tomography with simultaneous computed tomography for stage I and II Merkel cell carcinoma with concurrent sentinel lymph node biopsy staging: A single institutional experience from Westmead Hospital, Sydney

Background/Objective(18)F-fluorodeoxyglucose (FDG) positron emission tomography with simultaneous computed tomography (PET-CT) FDG PET-CT plays an important clinical role in the staging and management of Merkel cell carcinoma (MCC) although its role in stage I and II disease relative to a sentinel lymph node biopsy (SLNB) is undefined. This study aimed to compare the clinical impact of FDG PET-CT and SLNB on management in stage I and II MCC. MethodsThis was a retrospective observational study. Between 2000 and 2014, 65 patients with biopsy-proven MCC (all stages) underwent a staging FDG PET-CT as part of their investigations in Westmead Hospital, Sydney. Since 2006, 26 patients have had an SLNB and of these, 16 underwent both an SLNB and FDGPET-CT. All 16 patients had a histological diagnosis consistent with MCC without clinical evidence of regional or distant metastases prior to SLNB and FDG PET-CT (stages IB and IIB). These patients were assessed with respect to MCC staging and the subsequent change of patient management post-SLNB and FDG PET-CT. ResultsThe SLNB identified occult lymph node metastases in 10 patients (63%), with FDG PET-CT positive in only one patient (6%). Of the six SLNB-negative patients, none demonstrated additional metastases on the FDG PET-CT. ConclusionsIn patients with stage I and II MCC, FDG PET-CT is less sensitive than an SLNB in detecting occult metastatic lymph nodes. The routine use of FDG PET-CT in these patients may not be justified.