Introduction:Preoperative chemoradiotherapy(CRT),followed by total mesorectal excision,has become the standard of care for patients with clinical stages II and III rectal cancer.Patients with pathologic complete response(pCR) to preoperative CRT have been reported to have better outcomes than those without pCR.However,the factors that predict the response to neoadjuvant CRT have not been well defined.In this study,we aimed to investigate the impact of clinical parameters on the development of pCR after neoadjuvant chemoradiation for rectal cancer.Methods:A total of 323 consecutive patients from a single institution who had clinical stage II or III rectal cancer and underwent a long-course neoadjuvant CRT,followed by curative surgery,between 2005 and 2013 were included.Patients were divided into two groups according to their responses to neoadjuvant therapy:the pCR and non-pCR groups.The clinical parameters were analyzed by univariate and multivariate analyses,with pCR as the dependent variable.Results:Of the 323 patients,75(23.2%) achieved pCR.The two groups were comparable in terms of age,sex,body mass index,tumor stage,tumor location,tumor differentiation,radiation dose,and chemotherapy regimen.On multivariate analysis,a pretreatment carcinoembryonic antigen(CEA) level of <5 ng/mL[odds ratio(OR) = 2.170,95%confidence interval(CI) = 1.195-3.939,P = 0.011]and an interval of >7 weeks between the completion of chemoradiation and surgical resection(OR = 2.588,95%CI = 1.484-4.512,P = 0.001) were significantly associated with an increased rate of pCR.Conclusions:The pretreatment CEA level and neoadjuvant chemoradiotherapy-surgery interval were independent clinical predictors for achieving pCR.These results may help clinicians predict the prognosis of patients and develop adaptive treatment strategies. Introduction:Preoperative chemoradiotherapy(CRT), followed by total mesorectal excision,has become the standard of care for patients with clinical stages II and III rectal cancer.Patients with pathologic complete response(pCR) to preoperative CRT have been reported to have better outcomes than Those without pCR.However, the factors that predict the response to neoadjuvant CRT has not been well defined.In this study, we aimed to investigate the impact of clinical parameters on the development of pCR after neoadjuvant chemoradiation for rectal cancer.Methods:A total Of 323 consecutive patients from a single institution who had clinical stage II or III rectal cancer and underwent a long-course neoadjuvant CRT, followed by curative surgery,between 2005 and 2013 were included.Patients were divided into two groups according to their responses to neoadjuvant Therapy:the pCR and non-pCR groups.The clinical parameters were analyzed by univariate and multivariate analyses,with pCR as the dependent variable.Results:Of the 323 patients,75(23.2%) achieved pCR.The two groups were comparable in terms of age, sex,body mass index,tumor stage,tumor location,tumor differentiation,radiation dose,and chemotherapy regimen.On Multivariate analysis,a pretreatment carcinoembryonic antigen (CEA) level of <5 ng/mL[odds ratio(OR) = 2.170,95%confidence interval(CI) = 1.195-3.939,P = 0.011] and an interval of >7 weeks between The completion of chemoradiation and surgical resection (OR = 2.588, 95%CI = 1.484-4.512, P = 0.001) were significantly associated with an increased rate of pCR.Conclusions: The pretreatment CEA level and neoadjuvant chemoradiotherapy-surgery interval were independent clinical predictors For achieving pCR.These results may help clinicians predict the prognosis of patients and develop adaptive treatment strategies.