Correlation Between XRCC2 Expression And Preoperative Radiotherapy Sensitivity Of Rectal Cancer

Objective:To evaluate the role of XRCC2(X-ray repair cross complementing gene 2)protein in predicting the sensitivity of preoperative radiotherapy in rectal cancer by investigating its relationship with pathological response to preoperative chemoradiotherapy in rectal patients.Methods:A total of 88 cases of rectal adenocarcinoma admitted to The Affiliated Hospital of Qingdao University from Jan.2014 to Dec.2017 with preoperative chemoradiotherapy and operation treatment were selected.The primary outcomes measured were the expression levels of XRCC2 before and after chemoradiotherapy by immunohistochemistry and Real-time PCR(RT-PCR),as well as the association with clinicopathological characteristics and tumor regression grade.Results:Among the 88 patients,the average age was 58.6±9.0 years。And there were 17,58 and 13 patients with clinical TNM stage II,III and IV,respectively.Immunohistochemistry results show that following preoperative chemoradiotherapy,52 cases present a good pathologic response and 36 cases,a bad pathologic response.The sensitivity rate of radiochemotherapy was 59.1%,of which the pathologic complete response rate was 4.5%.XRCC2 protein expression before chemoradiotherapy was associated with preoperative tumor-nodes-metastasis(TNM)stage(P=0.020)and postoperative T stage(P=0.046).After chemoradiotherapy,the expression of XRCC2 protein was increased in 16 cases,decreased in 12 cases,and remained unchanged in 56 cases.There was no significant difference in the expression of XRCC2 protein before and after chemoradiotherapy(P>0.05).The sensitivity of radiotherapy for XRCC2 protein expression was 46.7% before radiotherapy and chemotherapy,and the sensitivity rate of radiotherapy for low expression was 85.7%.Single factor analysis of tumor pathological regression showed that XRCC2 expression before radiochemotherapy was found to significantly correlate with tumor pathological regression(P=0.001):the higher the expression of XRCC2 protein,the poorer the pathological response;the lower the expression of XRCC2 protein,the better the pathological response.There was no significant difference in gender,age,degree of differentiation,neurological invasion,vascular tumor thrombus related to the sensitivity of radiotherapy(P>0.05).The stratified analysis of patients with different degrees of pathological regression showed that the expression of XRCC2 protein in patients with complete pathological regression was significantly lower than that in patients with radiotherapy resistance(P=0.001).There was no significant difference in the expression of XRCC2 protein between the patients with complete regression and partial regression before chemoradiotherapy(P>0.05).Multivariate logistic regression analysis indicated that XRCC2 expression before chemoradiotherapy was the independent influencing factor of radiotherapy resistance(OR:6.857,95%CI:2.120~22.176).RT-PCR results show that XRCC2 mRNA expression level was associated with radiotherapy resistance before radiochemotherapy(P=0.01):those with high XRCC2 mRNA expression before radiochemotherapy was not sensitive to radiotherapy;those with low XRCC2 mRNA expression before radiochemotherapy was sensitive to radiotherapy.Conclusion:The expression of XRCC2 protein and mRNA is related to the sensitivity of preoperative radiotherapy for rectal cancer.Detecting of XRCC2 expression in biopsy specimens may be important for screening patients with sensitivity to preoperative radiotherapy for rectal cancer.