Quantitative FDG-PET/CT predicts local recurrence and survival for squamous cell carcinoma of the anus.

Purpose: ¹⁸ F-fluorodeoxyglucose (FDG) positron emission tomography-(PET)/computed tomography (CT) imaging is used for staging and treatment planning of patients with anal cancer. Quantitative pre- and posttreatment metrics that are predictive of recurrence are unknown. We evaluated the association between pre- and posttreatment FDG-PET/CT parameters and outcomes for patients with squamous cell carcinoma of the anus (SCCA).
Methods and Materials: The records of 110 patients treated between 2003 and 2013 with definitive radiation therapy for SCCA were reviewed under an institutional review board-approved protocol. The median radiation therapy dose was 50.4 Gy (range, 35-60 Gy). Concurrent chemotherapy was administered for 109 of 110 patients and generally consisted of 5-fluorouracil and mitomycin C (n = 94). All patients underwent pretreatment FDG-PET/CT and 101 of 110 underwent posttreatment FDG-PET/CT 3 months after completion of radiation therapy. The maximum standard uptake value (SUV _max ) was analyzed, in addition to multiple patient and treatment factors, by univariate and multivariate Cox regression for correlation with local recurrence (LR) and overall survival (OS).
Results: The median follow-up was 28.6 months. LR occurred in 1 of 15 (6.7%), 5 of 47 (10.6%), and 6 of 48 (12.5%) patients with stage I, II, and III disease, respectively. On univariate analysis, a significant association was observed between reduced LR and posttreatment SUV _max <6.1 ( P = .0095) and between increased OS and posttreatment SUV _max <6.1 ( P = .0086). On multivariate analysis, a significant association was observed between reduced LR and posttreatment SUV _max <6.1 ( P = .0013) and the use of intensity modulated radiation therapy ( P < .001). A significant multivariate association was observed between increased OS and posttreatment SUV _max <6.1 ( P = .0373) and the use of 5-fluorouracil/mitomycin C chemotherapy ( P = .001).
Conclusion: Posttreatment SUV _max <6.1 is associated with reduced LR and increased OS after chemoradiation therapy for SCCA independent of T and N stage on multivariate analysis. Greater follow-up is required to confirm this association with late patterns of failure.