Role of FDG-PET as predictive biomarker of pathologic complete response (pCR) in locally advanced rectal cancer (LARC) treated with capecitabine-based neoadjuvant chemoradiation (NACR).

e21118 Background: A favourable outcome is associated with pCR in LARC treated with NACR; pCR prediction through functional imaging may help the prospective evaluation of management strategies alternative to standard surgery. The aim of this prospective study was to identify whether FDG-PET activity and early/late response predicted independently pCR. Methods: Patients with histologically diagnosed cT3-4 and/or N+ primary rectal cancer were treated homogeneously with NACR (simultaneous boost technique radiotherapy 54 Gy on GTV/24 fractions plus capecitabine 1650 mg/mq/day) and total mesorectal excision 7-8 weeks later. FDG-PET uptake, expressed as maximum standardized uptake value, was obtained at baseline (SUV-1), at interim (2 weeks after treatment start: SUV-2) and 6 weeks after NARC completion (SUV-3) and was calculated as percentage difference (Δ-SUV). The role of SUV-1, SUV-2, SUV-3, Δ-SUV(1-2) and Δ-SUV(1-3) for pCR prediction was assessed using logistic regression analysis; ROC analysis was perfor...