Molecular response to neoadjuvant oxaliplatin and chemoradiation in rectal cancer: Molecular imaging (FDG-PET/CT), VEGFR, and EGFR expression and histopathologic correlations.

Abstract

e14012 Background: To analyze post-neoadjuvant molecular events assessed by FDG-PET/CT imaging and inmunohistochemical (IHC) determined by VEGFR and EGFR. To correlate molecular and pathological pattern of response. Methods: 41 patients (p) with cT3–4 induced with FOLFOX (2) and fluoropirimidin based neoadjuvant chemoradiation were staged and restaged with FDG-PET/CT (36p) and pre-/post-VEGFR and EGFR IHC determination (34p). Pathological response was assessed by Rodel's tumor regression grade (TRG) classification. Results: Neoadjuvant treatment significantly decreased the mean SUVmax at initial staging: 8.77 vs. 2.64 (p < 0.001). Reduction of FDG uptake (restaging SUVmax < 2) is correlated with T downstaging (p = 0.04) and favourable histopathological response (TGR = 3-4, p < 0.05). TGR responders have a significant superior reduction of tumor uptake (%SUVmax, ± SD): TGR responders −75.09% (± 18%) vs .TGR non responders -51.6% (± 36%), p = 0.05. VEGFR was expressed initially in all patients, except one, ...