RT Journal Article SR Electronic T1 15-Year Experience of 18F-FDG PET Imaging in Response Assessment and Restaging After Definitive Treatment of Merkel Cell Carcinoma JF Journal of Nuclear Medicine JO J Nucl Med FD Society of Nuclear Medicine SP 1328 OP 1333 DO 10.2967/jnumed.115.158261 VO 56 IS 9 A1 Keelan Byrne A1 Shankar Siva A1 Lori Chait A1 Jason Callahan A1 Mathias Bressel A1 Matthew Seel A1 Michael P. MacManus A1 Rodney J. Hicks YR 2015 UL http://jnm.snmjournals.org/content/56/9/1328.abstract AB The objective of this study was to evaluate the utility of 18F-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 18F-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 18F-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 18F-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. Conclusion: 18F-FDG PET imaging had a high impact on restaging after definitive treatment in patients with MCC. Metabolic response was significantly associated with overall survival. 18F-FDG PET may play an important role in ongoing post-treatment management of MCC.