Abstract
To investigate the association between (18)fluorine-2-deoxy-D-glucose positron emission tomography-computed tomography ((18)F-FDG PET/CT) parameters, serum carcinoembryonic antigen (CEA), and tumor response in patients with rectal cancer receiving neoadjuvant chemoradiotherapy (nCRT). Sixty-four patients with T3-4 and/or node-positive rectal cancer receiving nCRT followed by surgery were prospectively studied. PET/CT was performed before, and in 28 patients, both before and after nCRT. The pre-/post-nCRT maximum standardized uptake (SUVmax) values, differences between pre-/post-nCRT SUVmax (∆SUVmax), response index of SUVmax (RI-SUVmax), mean standardized uptake value (SUVmean), metabolic tumor volume (MTV), total lesion glycolysis (TLG), and CEA were measured. The ability of PET/CT parameters and CEA to predict Mandard's tumor regression grade (TRG) and pathological complete remission (pCR) were evaluated. 31 patients were identified as responders (TRG 1-2), and 19 exhibited pCR. For responders, significant differences were found for ΔSUVmax (24.88 vs. 15.39g/ml, p=0.037), RI-SUVmax (0.76 vs. 0.63, p=0.025), ΔSUVmean (14.43 vs. 8.65g/ml, p=0.029), RI-SUVmean (0.77 vs. 0.63, p=0.011), CEA-pre (6.30 vs. 27.86μg/L, p<0.001), CEA-post (2.22 vs. 5.49μg/L, p=0.002), ΔCEA (4.08 vs. 23.13μg/L, p<0.001), and RI-CEA (0.25 vs. 0.55, p=0.002). Differences between pCR and non-pCR patients were noted as RI-SUVmean (0.77 vs. 0.65, p=0.043), MTV-pre (9.87 vs. 14.62cm(3), p=0.045), CEA-pre (5.62 vs. 22.27μg/L, p=0.002), CEA-post (1.95 vs. 4.72μg/L, p=0.001), and ΔCEA (3.68 vs. 17.99μg/L, p=0.013). Receiver operating characteristic analysis revealed that RI-SUVmean exhibited the greatest accuracy in predicting responders, whereas CEA-post and ΔCEA exhibited the greatest accuracy in predicting pCR. (18)F-FDG PET/CT parameters and CEA are accurate tools for predicting tumor response to nCRT in rectal cancer.
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