587P - Carbohydrate Antigen 19-9 Levels Associated with Pathological Responses to Preoperative Chemoradiotherapy in Rectal Cancer

Abstract

ABSTRACT Aim: To investigate whether pretreatment serum carbohydrate antigen 19-9 (CA 19-9) levels are associated with pathological responses to preoperative chemoradiotherapy (CRT) in patients with rectal cancer. Methods: In total, 260 patients with locally advanced rectal cancer (cT3 4NanyM0) who underwent preoperative CRT and radical surgery were analyzed retrospectively. CRT consisted of 50.4 Gy pelvic radiotherapy and concurrent chemotherapy. Radical surgery was performed at median 7 weeks after CRT completion. Pathological CRT response criteria included downstaging (ypStage 0-I) and ypT0-1. A discrimination threshold of CA 19-9 level was determined using a receiver operating characteristics analysis. A multivariate logistic regression model was constructed to identify factors independently associated with pathological CRT responses. Results: The median CA 19-9 level was 8.0 (1.0-648.0) U/mL. Downstaging occurred in 94 (36.2%) patients and ypT0-1 in 50 (19.2%). The calculated optimal threshold of CA 19-9 level was 10.2 U/mL for downstaging and 9.0 U/mL for ypT0-1. On univariate analysis, tumor size, cT classification, carcinoembryonic antigen (CEA), and CA 19-9 showed significant associations with downstaging. Tumor size, cN classification, histological grade, CEA, and CA 19-9 were significantly associated with ypT0-1. A CA 19-9 level of ≤ 10.0 U/mL or ≤ 9.0 U/mL was a positive predictor of downstaging and ypT0-1. On multivariate analysis, CA 19-9 (≤ 9.0 U/mL) was significantly associated with downstaging (odds ratio, 2.089; 95% confidence interval, 1.189-3.669; P = 0.010) or ypT0-1 (OR, 2.207; 95% CI, 1.079-4.512; P = 0.030), independent of clinical stage or CEA. Conclusions: This study firstly showed a significant association of pretreatment serum CA 19-9 levels with pathological CRT responses of rectal cancer. Disclosure: All authors have declared no conflicts of interest.