Role of ¹⁸F-FDG PET/CT in Posttreatment Evaluation of Anal Carcinoma

The aim of this study was to evaluate the relevance of PET/CT and ¹⁸F-FDG as a strategy for response evaluation after chemoradiotherapy for anal cancer. For this, the performance of posttreatment ¹⁸F-FDG PET/CT, the impact on patient care, and the predictive value of metabolic response were assessed. Methods: This was a retrospective and multicenter analysis of 87 patients treated by chemoradiotherapy for anal squamous cell carcinoma between October 2007 and October 2013. All patients underwent systematic posttreatment ¹⁸F-FDG PET/CT and were followed with at least a clinical examination every 4 mo for 2 y and every 6 mo thereafter. Disease progression was confirmed by biopsy for all patients in the case of local recurrence before surgery. Kaplan-Meier and Cox regression models were used to test for associations between metabolic or clinical endpoints and progression-free survival (PFS) or cause-specific survival (CSS). Results: The median follow-up was 25 mo. ¹⁸F-FDG PET/CT was performed 1-8 mo (median, 4 mo) after completion of chemoradiotherapy. Overall, 25 patients relapsed and 13 died. The posttherapy ¹⁸F-FDG PET/CT did not show any abnormal ¹⁸F-FDG uptake (complete metabolic response [CMR]) in 55 patients whereas 32 displayed incomplete response (non-CMR): 15 patients with partial response and 17 with disease progression. The sensitivity of ¹⁸F-FDG PET/CT to detect residual tumor tissue was 92% (95% confidence interval [CI], 75%-97%), specificity was 85% (95% CI, 75%-92%), positive predictive value was 72% (95% CI, 61%-90%), and negative predictive value was 96.4% (95% CI, 90%-98.7%). The 2-y PFS was 96% (95% CI, 90-100) for patients with CMR and 28% (95% CI, 14-47) for non-CMR patients (P < 0.0001). The 2-y CSS was 100% for patients with CMR and 59% (95% CI, 42-84) for those without CMR (P < 0.0001). ¹⁸F-FDG PET/CT changed patient management in 14 cases (16%), with relevant modifications in 12 (14%). A Cox proportional hazards model of survival outcome indicated that a CMR was the only significant predictor of PFS and CSS (P < 0.0001). Conclusion:¹⁸F-FDG PET/CT shows good accuracy in posttreatment evaluation of anal cancer and has a relevant impact on patient management. Moreover, CMR is associated with good survival outcome. Thus, ¹⁸F-FDG PET/CT may play a significant role during posttreatment follow-up of anal cancer.