To explore the efficacy of neoadjuvant therapy in patients with advanced rectal cancer, and to find pathological and clinical factors that can predict pathological complete response of neoadjuvant therapy.

A retrospective analysis was conducted in 129 patients with rectal cancer who underwent neoadjuvant therapy and total mesorectal resection at Shanxi Cancer Hospital from June 2018 to December 2020. According to their response to neoadjuvant therapy (postoperative pathological results), they were divided into two groups of pathological complete response (pCR) and non- pathological complete response(non-pCR). Statistical analysis was performed on several indicators of gender, age, distance from the tumor to the anal verge, preoperative T stage, N stage, CEA level before treatment, maximum tumor diameter, microsatellite status, and preoperative combined radiotherapy.

A total of 129 patients were included, including 15 patients (11.6%) with pCR after neoadjuvant therapy. Univariate analysis showed that the proportion of patients with low preoperative CEA level in pCR after neoadjuvant therapy (21.3%) was significantly higher than that in patients with high CEA level (2.9%), and the proportion of patients with preoperative combined chemoradiotherapy (23.1%) was significantly higher in pCR than that in patients with preoperative chemotherapy alone (6.7%) (χ²=5.623, P＜0.05); the proportion of pCR in patients with microsatellite stability (12.3%) was numerically higher than that in patients with microsatellite instability (6.7%) (P＞0.05). Logistic regression analysis showed that high CEA level before treatment (OR=12.570, 95%CI: 2.515~62.830) and preoperative combined chemoradiotherapy (OR=6.319, 95%CI: 1.850~21.580) were associated with pCR after neoadjuvant therapy independent factor. The ROC curve, it was found that the best cut-off value of the logistic regression model to predict the pCR rate was 0.87, the sensitivity was 0.82, the specificity was 0.87, and the AUC value was 0.885. Preoperative CEA <2.315 μg/L was an effective indicator to predict pCR with neoadjuvant therapy.

CEA level before treatment and preoperative combined chemoradiotherapy can be used as reference indicators for clinical evaluation of the efficacy of neoadjuvant therapy. Microsatellite status was not found to be an independent prognostic factor for pCR after neoadjuvant therapy for rectal cancer.