title: 18F-FDG PET provides high-impact and powerful prognostic stratification in the staging of Merkel cell carcinoma: a 15-year institutional experience.
abstract: Merkel cell carcinoma (MCC) is a rare but aggressive skin cancer with limited evidence on the role of PET scanning. The primary aim of this study was to assess the impact of (18)F-FDG PET in the staging and management of MCC.
  
  
  METHODS
  A single-institution review using clinical outcome data collected until February 2012 was performed of patients with MCC who underwent staging PET scanning between January 1997 and October 2010. Management plans were recorded prospectively at the time of the PET request, and follow-up outcomes were recorded retrospectively. The clinical impact of PET was scored using our previously published criteria: "high" if the PET scan changed the primary treatment modality or intent; "medium" if the treatment modality was unchanged but the radiation therapy technique or dose was altered. The primary objective was to test the hypothesis that the true proportion of patients who have a high- or medium-impact scan would be greater than 25%.
  
  
  RESULTS
  The median follow-up of 102 consecutive patients was 4.8 y. The results of staging PET had an impact on patient management in 37% of patients (P < 0.003). High- and medium-impact scans were recorded for 22% and 15% of patients, respectively. PET staging results differed from conventional staging results in 22% 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%), respectively. In stratification by PET-defined stage, the 5-y overall survival was 67% for patients with stage I/II disease but only 31% for patients with stage III disease (log-rank P < 0.001). The 5-y cumulative incidence of locoregional failure, distant failure, and death was 16.6%, 22.3% and 14.3%, respectively. On multivariate analysis, only PET stage (P < 0.001) and primary treatment modality (P = 0.050) were significantly associated with overall survival. The primary treatment modality was not associated with progression-free survival when stratification was by tumor stage.
  
  
  CONCLUSIONS
  The use of (18)F-FDG PET scans had a great impact on patients and may play an important role in the prognostic stratification and treatment of this disease.
authors.affiliation: Sir Peter MacCallum Department of Oncology, University of Melbourne, Melbourne, Australia. shankar.siva@petermac.org
authors.forename: Shankar
authors.initials: S
authors.lastname: Siva
authors.forename: Keelan
authors.initials: K
authors.lastname: Byrne
authors.forename: Matthew
authors.initials: M
authors.lastname: Seel
authors.forename: Mathias
authors.initials: M
authors.lastname: Bressel
authors.forename: Daphne
authors.initials: D
authors.lastname: Jacobs
authors.forename: Jason
authors.initials: J
authors.lastname: Callahan
authors.forename: Joshua
authors.initials: J
authors.lastname: Laing
authors.forename: Michael P
authors.initials: MP
authors.lastname: Macmanus
authors.forename: Rodney J
authors.initials: RJ
authors.lastname: Hicks
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D015266:Carcinoma, Merkel Cell / Q000000981:diagnostic imaging* / Q000473:pathology* / Q000628:therapy; D019788:Fluorodeoxyglucose F18; D006801:Humans; D008875:Middle Aged; D009367:Neoplasm Staging; D049268:Positron-Emission Tomography; D011379:Prognosis; D012189:Retrospective Studies; D012878:Skin Neoplasms / Q000000981:diagnostic imaging* / Q000473:pathology* / Q000628:therapy; D016019:Survival Analysis; D017211:Treatment Failure
chemical_list: D019788:Fluorodeoxyglucose F18
keywords: Merkel cell carcinoma; positron emission tomography; staging