Objective:To assess the response rate of patients with rectal adenocarcinoma to neoadjuvant therapy and to identify the predictors of histological regression after neoadjuvant radiotherapy(RT)or concurrent chemoradiotherapy(CCRT).Methods:This study recruited 64 patients.The patients had resectable cancer of the lower and the middle rectum(T3/T4 and/or N+)without distant metastasis and received neoadjuvant RT or CCRT followed by radical surgery with total mesorectal excision(TME)between January 2006 and December 2011.The patients were classified into non-response(NR),partial response(PR),and pathologic complete response(p CR)based on the Dworak tumor regression grading system.Results:The median age of patients was 57 years(ranging from 22 to 85).A total of 24 patients were treated with neoadjuvant CCRT,whereas 40 patients were treated with RT alone.Abdominoperineal resection(APR)was performed on 29 patients(45%).Anterior resection with TME was performed on 34 patients(53%).One patient had local resection.Histologically,12(19%),24(73%),and 28(44%)patients exhibited p CR,PR,and NR,respectively.Univariate analysis revealed that the predictors of tumor regression were as follows:the absence of lymph node involvement from initial imaging(c N0)(P=0.021);normal initial carcinoembryonic antigen(CEA)level(P=0.01);hemoglobin level≥12 g/dl(P=0.009);CCRT(P=0.021);and tumor downstaging in imaging(P=0.001).Multivariate analysis showed that the main predictors of p CR were CT combined with neoadjuvant RT,c N0stage,and tumor regression on imaging.Conclusions:Identifying the predictors of p CR following neoadjuvant therapy aids the selection of responsive patients for nonaggressive surgical treatment and possible surveillance. Objective: To assess the response rate of patients with rectal adenocarcinoma to neoadjuvant therapy and to identify the predictors of histological regression after neoadjuvant radiotherapy (RT) or concurrent chemoradiotherapy (CCRT). Methods: This study recruited 64 patients. The patient had resectable cancer of the lower and the middle rectum (T3 / T4 and / or N +) without distant metastasis and received neoadjuvant RT or CCRT followed by radical surgery with total mesorectal excision (TME) between January 2006 and December 2011.The patients were classified into non-response (NR), partial response (PR), and pathologic complete response (p CR) based on the Dworak tumor regression grading system. Results: The median age of patients was 57 years (ranging from 22 to 85) were treated with neoadjuvant CCRT, whereas 40 of the 40 patients were treated with RT alone. One patient h (42%). One patient h ad local resection. Histologically, 12 (19%), 24 (73%), and 28 (44%) patients showed p CR, PR, and NR, respectively. Univariate analysis revealed that the predictors of tumor regression were as follows: the absence of lymph node involvement from initial imaging (c N0) (P = 0.021); normal initial carcinoembryonic antigen (CEA) level (P = 0.01); hemoglobin level≥12 g / dl ); and tumor downstaging in imaging (P = 0.001). Multivariate analysis showed that the main predictors of pCR were CT combined with neoadjuvant RT, c N Estage, and tumor regression on imaging. Conflusions: Identifying the predictors of pCR following neoadjuvant therapy aids the selection of responsive patients for nonaggressive surgical treatment and possible surveillance.