AimWe aimed to investigate the value of PET-CT in therapy response and the correlation of quantitative PET parameters with histopathologic results in patients with locally advanced rectal cancer (LARC) before and after neoadjuvant chemoradiotherapy. We also analyzed the correlation of PET-CT parameters between Ki-67 and glucose transporter 1 (GLUT1).Patients and methodsA total of 29 patients diagnosed with LARC who had undergone a biopsy between 2009 and 2012 were included in our study. Quantitative PET parameters [standardized uptake value (SUV)(max-mean), lean body mass SUVmax-mean, tumor/liver SUV, retention index , and SUVmax] were measured before and after therapy using PET-CT. Tumor regression grade (TRG) was evaluated according to Wheeler's classification. Patients in grade 1 were considered responders, whereas patients at grades 2 and 3 were considered nonresponders. Immunohistochemical staining with Ki-67 and GLUT1 was performed on biopsy and surgical specimens. The correlation between staining ratios and SUV was also investigated.ResultsSUV parameters were significantly decreased after therapy (P<0.001). Twelve (41%) patients were at TRG1, 10 (35%) were at TRG2, and seven (24%) were at TRG3. A cutoff SUVmax of 5.05 to discriminate between responders and nonresponders after treatment revealed a sensitivity of 57%, specificity of 73%, negative predictive value of 65%, positive predictive value of 67%, and accuracy of 66%. Using a cutoff of 3.55 for the SUVmean (standardized measurement of SUV with 1.2-cm-diameter region of interest) revealed a sensitivity, specificity, negative predictive value, positive predictive value, and accuracy of 67, 76, 67, 76, and 72%, respectively. For a cutoff of 1.95 for the tumor SUVmean/liver SUVmean, these diagnostic values after therapy were 73, 78, 82, 67, and 76%, respectively. We found a moderate correlation between liver-based SUVmax (r=-0.35, P=0.019) and SUVmean (r=-0.31, P=0.036) with GLUT1 after therapy. Quantitative PET parameters and retention index were moderately correlated with Ki-67.ConclusionPET-CT is a useful method for assessing the response to neoadjuvant chemoradiotherapy in patients with LARC. The most significant parameter for assessing treatment response using SUV parameters is the tumor/liver ratio. Copyright (C) 2015 Wolters Kluwer Health, Inc. All rights reserved.