Prognostic Analysis And Beneficiary Exploration Of Postoperative Radiotherapy For Stage PT4M0 Sigmoid Colon Cancer

Objective: To explore the prognostic value and beneficiary of postoperative radiotherapy for patients with non-metastatic pathologic stage T4 sigmoid colon cancer,providing the basis for the formulation of clinical treatment strategy.Methods: The clinicopathological data of 4,979 patients with pathologic stage T4M0 sigmoid colon cancer in the Surveillance,Epidemiology,and End Results(SEER)database from 2004 to 2016 were retrospectively analyzed,and multivariate analysis and subgroup analysis were used to explore the effect of postoperative radiotherapy on overall survival(OS).A total of 208 patients with pathologic stage T4M0 sigmoid colon cancer were analyzed retrospectively at our institute from January 2010 to December 2016.Cox regression risk score model was developed to screen the high-risk groups of postoperative locoregional recurrence.All patients received radical surgery.Results: According to different treatment strategies,4,979 patients in the SEER database were divided into the surgery combined with radiotherapy group(430 cases,8.6%)and the surgery group(4,549 cases,91.4%).Propensity score matching(PSM)was performed according to the ratio of surgery combined with radiotherapy group to surgery group equal to 1:2,and the matching factors included age,differentiation,tumor size,T stage,and N stage.Both before PSM and after PSM,postoperative radiotherapy could significantly prolong the OS(all P<0.05).After PSM,the 1-,3-,and 5-year OS rates of surgery combined with radiotherapy group and surgery group were 94.6% vs.87.9%,71.4% vs.67.4%,and 60.4% vs.54.6%,respectively.And the median OS was 86 months and 74 months,respectively.Multivariate analysis showed that postoperative radiotherapy was an independent predictor of OS(hazard ratio [HR]=1.529,95% confidence interval [CI]: 1.194-1.996,P=0.004).Subgroup analysis showed that patients with poorly differentiated or undifferentiated tumors,tumor size ≥5cm,or stage T4 b were the beneficiaries of postoperative radiotherapy(all P<0.05).Among 208 patients in our hospital,57 cases(27.4%)had locoregional recurrence,including 14 cases of anastomotic site recurrence and 43 cases of abdominal or pelvic lymph node recurrence.The median recurrence time was 11 months.The OS in the relapsed group was significantly lower than that in the nonrelapsed group(P<0.001).208 patients were randomly divided into training set and validation set according to the ratio of 1:1.Multivariate analysis of the training set showed that serum carcinoembryonic antigen(CEA),differentiation,lymph node dissection number,and N stage were correlated with locoregional recurrence-free survival(LRRFS).A postoperative locoregional recurrence risk scoring model was constructed based on serum CEA,differentiation,lymph node dissection number,and N stage.Patients were classified as high-risk of recurrence if the total score was greater than or equal to 6.5.The LRRFS and OS in the high-risk group were significantly lower than those in the low-risk group(all P<0.001).In the validation set,LRRFS and OS were also found to be lower in the high-risk group than in the low-risk group(all P<0.001).Conclusions: Postoperative radiotherapy for pathologic stage T4M0 sigmoid colon cancer can significantly prolong the OS.Postoperative radiotherapy is recommended for potential beneficiaries,especially the patients with high-risk locoregional recurrence.