PT - JOURNAL ARTICLE AU - Sonia Mahajan AU - Christopher A. Barker AU - Audrey Mauguen AU - Sandra P. D'Angelo AU - Randy Yeh AU - Neeta Pandit-Taskar TI - <sup>18</sup>F-FDG PET/CT for post-treatment surveillance imaging of patients with stage III Merkel cell carcinoma AID - 10.2967/jnumed.121.262882 DP - 2021 Oct 01 TA - Journal of Nuclear Medicine PG - jnumed.121.262882 4099 - http://jnm.snmjournals.org/content/early/2021/10/07/jnumed.121.262882.short 4100 - http://jnm.snmjournals.org/content/early/2021/10/07/jnumed.121.262882.full AB - To investigate diagnostic and prognostic value of 18F-FDG PET/CT for surveillance imaging in patients treated for Stage III Merkel cell carcinoma (MCC). Methods: This retrospective study included 61 consecutive stage III MCC patients, who were clinically asymptomatic and underwent surveillance FDG-PET/CT. Findings were correlated with either pathology and/or clinical/imaging follow-up. Median follow-up period was 4.8 years. Statistical analyses were performed. Results: FDG-PET/CT detected unsuspected recurrences in 33% patients (20/61) with lesion-based sensitivity, specificity, and accuracy of 92%, 93%, and 93%, respectively. Mean±SD SUV for malignant and benign lesions was 7.5±3.9 and 3.8±2.0, respectively. Unknown distant metastases, as first recurrence site, were noted in 12 of 61 patients. Those with positive disease on FDG-PET/CT within one year of definitive treatment had relatively worse overall survival (p&lt;0.0001). After adjustment on stage, risk of death increased with higher SUVmax (HR for one unit=1.17;P = 0.006) and with a higher number of positive lesions on FDG-PET/CT (HR for one additional lesion = 1.60;p&lt;0.001). Conclusion: Post-definitive treatment surveillance FDG-PET/CT scan detects unsuspected recurrences and has prognostic value. Inclusion of FDG-PET/CT within the first 6 months after definitive treatment would be appropriate for surveillance and early detection of recurrence. Our data merits further studies to evaluate the prognostic implications.