title: 15-Year Experience of 18F-FDG PET Imaging in Response Assessment and Restaging After Definitive Treatment of Merkel Cell Carcinoma.
abstract: The objective of this study was to evaluate the utility of (18)F-FDG PET in restaging and response assessment of patients who underwent definitive treatment for Merkel cell carcinoma (MCC).
  
  
  METHODS
  A retrospective review of patients undergoing (18)F-FDG PET imaging for MCC between January 1997 and October 2010 at the Peter MacCallum Cancer Centre with follow-up until February 2015 was performed. Data analysis was performed on patients who were treated definitively and underwent post-treatment PET imaging performed either as a restaging scan for ongoing monitoring, suspicion of recurrence, or assessment for suitability of salvage treatment or as response assessment within 1-6 mo of treatment. Management plans were recorded prospectively before (18)F-FDG PET imaging and compared with post-imaging management to assess the impact of the study as per our previously defined categories: high if the primary treatment modality or intent was changed and medium if the radiotherapy technique or dose was altered. In total, 62 patients were included in the analysis. Thirty-six patients underwent 53 restaging scans, and 37 patients underwent a response-assessment scan. The median follow-up of patients in the restaging group was 5.3 y (95% confidence interval [CI], 4.6-9.4), and it was 5.7 y (95% CI, 4.3-10.8) in the response-assessment group.
  
  
  RESULTS
  Restaging (18)F-FDG PET scans had a high impact in 24 of 53 cases (45%) and a medium impact in 6 of 53 cases (11%). In the response-assessment group, 24 of 37 patients had a complete metabolic response (CMR). Patients without a CMR had a 15% 1-y overall survival (95% CI, 0.04-0.55). Those with a CMR had an 88% 2-y overall survival (95% CI, 0.75-1.00) and a 68% 5-y overall survival (95% CI, 0.49-0.95). The presence of a CMR (P < 0.001) and nodal involvement (P = 0.016) were statistically significant prognostic factors for overall survival.
  
  
  CONCLUSIONS
  (18)F-FDG PET imaging had a high impact on restaging after definitive treatment in patients with MCC. Metabolic response was significantly associated with overall survival. (18)F-FDG PET may play an important role in ongoing post-treatment management of MCC.
authors.affiliation: Department of Radiation Oncology, Peter MacCallum Cancer Centre, Melbourne, Australia.
authors.forename: Keelan
authors.initials: K
authors.lastname: Byrne
authors.affiliation: Department of Radiation Oncology, Peter MacCallum Cancer Centre, Melbourne, Australia Sir Peter MacCallum Department of Oncology, The University of Melbourne, Melbourne, Australia shankar.siva@petermac.org.
authors.forename: Shankar
authors.initials: S
authors.lastname: Siva
authors.affiliation: University of Notre Dame, Sydney, Australia.
authors.forename: Lori
authors.initials: L
authors.lastname: Chait
authors.affiliation: Department of Cancer Imaging, Peter MacCallum Cancer Centre, Melbourne, Australia.
authors.forename: Jason
authors.initials: J
authors.lastname: Callahan
authors.affiliation: Department of Biostatistics and Clinical Trials, Peter MacCallum Cancer Centre, Melbourne, Australia; and.
authors.forename: Mathias
authors.initials: M
authors.lastname: Bressel
authors.affiliation: Department of Radiation Oncology, Waikato Regional Cancer Centre, Hamilton, New Zealand.
authors.forename: Matthew
authors.initials: M
authors.lastname: Seel
authors.affiliation: Department of Radiation Oncology, Peter MacCallum Cancer Centre, Melbourne, Australia Sir Peter MacCallum Department of Oncology, The University of Melbourne, Melbourne, Australia.
authors.forename: Michael P
authors.initials: MP
authors.lastname: MacManus
authors.affiliation: Sir Peter MacCallum Department of Oncology, The University of Melbourne, Melbourne, Australia Department of Cancer Imaging, Peter MacCallum Cancer Centre, Melbourne, Australia.
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* / Q000628:therapy*; D005260:Female; D019788:Fluorodeoxyglucose F18; D005500:Follow-Up Studies; D006801:Humans; D008137:Longitudinal Studies; D008297:Male; D008875:Middle Aged; D063868:Patient Outcome Assessment; D049268:Positron-Emission Tomography / Q000379:methods*; D011379:Prognosis; D019275:Radiopharmaceuticals; D012189:Retrospective Studies; D012878:Skin Neoplasms / Q000000981:diagnostic imaging* / Q000628:therapy*; D016019:Survival Analysis; D015996:Survival Rate; D016896:Treatment Outcome
chemical_list: D019275:Radiopharmaceuticals; D019788:Fluorodeoxyglucose F18
keywords: 18F-FDG PET; Merkel; post-treatment; response; salvage