18F-FDG PET Provides High-Impact and Powerful Prognostic Stratification in the Staging of Merkel Cell Carcinoma: A 15-Year Institutional Experience

F-FDG PET in the stag-ing and management of MCC. Methods: A single-institution reviewusing clinical outcome data collected until February 2012 was per-formed of patients with MCC who underwent staging PET scanningbetween January 1997 and October 2010. Management plans wererecorded prospectively at the time of the PET request, and follow-up outcomes were recorded retrospectively. The clinical impact ofPET was scored using our previously published criteria: “high” if thePET scan changed the primary treatment modality or intent; “me-dium” if the treatment modality was unchanged but the radiationtherapy technique or dose was altered. The primary objective wasto test the hypothesis that the true proportion of patients who havea high- or medium-impact scan would be greater than 25%.Results: The median follow-up of 102 consecutive patients was4.8 y. The results of staging PET had an impact on patient manage-ment in 37% of patients (P , 0.003). High- and medium-impactscans were recorded for 22% and 15% of patients, respectively.PET staging results differed from conventional staging results in22% of patients, with PET upstaging 17% and downstaging 5%.The 3- and 5-y overall survival was 60% (95% confidence interval,50%–71%) and 51% (95% confidence interval, 41%–64%), respec-tively. In stratification by PET-defined stage, the 5-y overall survivalwas 67% for patients with stage I/II disease but only 31% forpatients with stage III disease (log-rank P , 0.001). The 5-y cumu-lativeincidence of locoregional failure, distant failure, and death was16.6%, 22.3% and 14.3%, respectively. On multivariate analysis,only PET stage (P , 0.001) and primary treatment modality (P 50.050) were significantly associated with overall survival. The pri-mary treatment modality was not associated with progression-freesurvival when stratification was by tumor stage. Conclusion: Theuse of