Predictors of pathologic complete response after neoadjuvant chemoradiotherapy for locally advanced rectal cancer

Abstract

Objective To evaluate the potential influencing factors associated with pathologic complete response (pCR) after neoadjuvant chemoradiotherapy for locally advanced rectal cancer (LARC). Methods A retrospective analysis was performed on the clinical data 265 patients with stage Ⅱ and Ⅲ(the 7th version of AJCC) rectal cancer admitted to our hospital from 2011 to 2013. All patients underwent neoadjuvant concurrent chemoradiotherapy (CCRT) followed by surgery with/or without induction chemotherapy during the interval between the complete of CCRT and surgery. The predictors associated with pCR were analyzed by univariate and multivariate logistic regression analyses. With the use of the independent predictive variables for pCR from multivariate analysis, a clinical risk score model was established according to the following criteria: no-risk group (0 factor); low-risk group (1 factor); high-risk group (2 factors). Results Among these 265 patients, 50(18.9%) achieved pCR. The univariate analysis showed that carcinoembryonic antigen (CEA) level before CCRT (P=0.017), T stage before CCRT (P=0.001), interval between complete of CCRT and surgery (P=0.000), and the maximum tumor thickness before CCRT (P=0.040) were significantly associated with pCR. The multivariate analysis showed that pre-CCRT CEA level (P=0.021 or 0.446) and interval between the complete of CCRT and surgery (P=0.000 or 3.774) were significant predictors of pCR. When stratifying for smoking status, only low pre-CCRT CEA level was significantly associated with pCR in the non-smoking patients (P=0.044). For the prediction of pCR by the clinical risk score model, the sensitivity was 0.805, the specificity was 0.460, the area under the receiver operating curve was 0.690(95% CI=0.613-0.767), the positive predictive value was 35.49%, the negative predictive value was 86.5%, and the predictive accuracy was 73.9%. Conclusions For locally advanced rectal cancer, pCR can be achieved in some patients after neoadjuvant therapy. Low pre-CCRT CEA level and long interval time between CCRT and surgery are independent factors associated with pCR, and only low pre-CCRT CEA level is an associated factor in the group of nonsmokers. The clinical risk score model based on pre-CCRT CEA level>5 ng/ml and time interval from CCRT completion to surgery ≤8 weeks can be used to predict pCR after neoadjuvant chemoradiotherapy for LARC. Key words: Rectal neoplasms/neoadjuvant therapy; Pathologic complete response; Factors analysis