摘要Objective The aim of this study was to evaluate the impact of serum carcinoembryonic antigen (CEA) in the prediction of pathological complete response (pCR) in locally advanced rectal cancer (LARC) patients treated with neoadjuvant chemoradiotherapy (nCRT). Methods A total of 925 LARC patients who underwent nCRT followed by TME between March 2006 and February 2018 were enrolled at Fudan University Shanghai Cancer Center. Using logistic regression models, we investigated the associations between serum CEA levels and pathological complete remission (pCR). Further stratified analyses were performed according to different CEA thresholds. Results We found that pre-nCRT CEA and post-nCRT CEA were negatively correlated with pCR (P < 0.001). Stratified analyses revealed that when the CEA cutoff value was set to 5 ng/mL, 10.6％ of patients with post-nCRT CEA levels > 5 ng/mL achieved pCR. Meanwhile, when the CEA cutoff value was set to 10 ng/mL, only 6.8％ of the patients with post-nCRT CEA levels > 10 ng/mL achieved pCR. Conclusion In summary, pre- and post-nCRT CEA levels ≤ 5 ng/mL were favorable predictors of pCR in LACR patients, and the "watch and wait" strategy is not recommended for patients with post-nCRT CEA levels > 10 ng/mL.