| Background:As treatment techniques have matured,clinical practitioners have placed more emphasis on prognosis.After total rectal mesenteric resection for rectal cancer,positive circumferential margins are associated with a high risk of local recurrence and distant metastasis.The anterior portion of the rectal mesentery is thinner than the lateral portion,and the risk of positive anterior tumor margins may be higher than that of lateral tumors.This anatomical factor may have an impact on prognosis and thus determine the postoperative treatment plan for patients.Few previous relevant studies have clarified whether this influence effect exists.We sought to clarify the impact of tumor location around the rectum on the treatment and prognosis of patients with cancer treated by total rectal mesenteric resection.Purpose:To compare the positive margin incision rate,postoperative complication rate and patient survival of low rectal cancer with different circumferential cancer locations,and to construct a risk prediction model to guide clinically relevant treatment.Method:The study was retrospectively analyzed by selecting 272 patients operated for low rectal cancer from the time period of January 2015-December 2017 strictly according to the inclusion and exclusion criteria.The distance of the cancer from the anal verge was determined according to electronic colonoscopy and was considered for inclusion in the study if it was less than 6 cm.Tumor location was classified as anterior,posterior,and lateral location,with 89 cases in the anterior group,92 cases in the posterior group,and 91 cases in the lateral group.All patients underwent TME for rectal cancer and none had preoperative neoadjuvant chemotherapy.General patient data were collected: name,age,gender,height,weight,CEA,ASA classification,time of surgery,pathological T-stage,number of lymph node metastases,distance from the lower edge of the tumor to the anal edge,circumferential cancer location,postoperative pathology,number of positive margin cases,complications,and contact number.Prognostic follow-up information: overall survival time,follow-up time,recurrence and recurrence time.After using propensity score matching method for anterior,posterior and lateral groups,The positive margin rate and complication rate were measured by gathering the cases of positive margins and the number of complications in each group.The difference between the two groups was compared using the chi-square test or the continuous corrected chi-square test.KM(Kaplan-Meier)survival curves were used to analyze the effect of different circumferential tumor locations on survival;We used single and multifactor cox regression analysis to ascertain factors associated with postoperative patient survival.All cases were randomly divided into a training dataset(n=212)and a validation dataset(n=60)in the ratio of 8:2.The training set was used to construct a prediction model for 3-year and 5-year survival after TME for low rectal cancer using the risk factors identified by survival analysis.The validation dataset was then subjected to internal validation.Model precision was measured by the receiver operating characteristic curve(ROC),the area under the curve(AUC),and the C-index.Additionally,calibration curves were applied to contrast the concordance between the predicted and observed likelihoods of the model.Result:Seventy-one matched groups were obtained after propensity score matching,with71 cases in the anterior group,posterior group and lateral group.The rates of positive circumferential resection margin in the matched anterior,posterior and lateral groups were 6.6%,9% and 3.4%,respectively;the rates of positive circumferential resection margin in the matched anterior and lateral groups were 7.0% and 1.4%(P<0.05),whereas the rates of positive circumferential resection margin in the posterior and lateral wall groups were 3.4% and 2.8%(P=0.681),with no statistical difference in the results.The complication rates were 15.4%,15.2%,and 9.0% in the matched anterior,posterior,and lateral groups,respectively,and 15.5% and 8.5% in the matched anterior and lateral groups(P=0.196),11.3% and 8.5% in the posterior and lateral groups(P=0.577),and 13.7% and 9.6%(P=0.439),with a non-statistically significant difference.After matching,the 3-year survival rates were 64.23% and 72.69% for anterior and lateral tumor,and the 5-year survival rates were 53.84% and 64.04%,with statistically significant differences(P<005);while the 3-year survival rates were 73.97%and 74.14% for posterior and lateral tumor(P=0.344),and the 5-year survival rates were 57.61% and 62.55%(P= 0.284);3-year survival rates for anterior and posterior tomor were 68.87% and 72.33%(P=0.328),and 5-year survival rates were 55.90% and59.06%(P=369).The results were not statistically different.Kaplan-Meier analysis suggested that anterior tumor could affect postoperative survival(P=0.005).Multifactorial cox regression analysis revealed that age,T-stage,anterior tumor,circumferential margin,and complications were risk factors affecting postoperative survival in patients with low rectal cancer(P<0.05).In the constructed prediction model for postoperative survival in low-grade rectal cancer,the AUC values of 3-year and 5-year survival probabilities in the training dataset were 0.719 and 0.751 respectively.In the validation dataset,the AUC values of 3-year and 5-year were 0.702 and 0.777,respectively,and the AUC results indicated that the accuracy of the column line plot was better(AUC>0.7).The calibration curve results indicate that the prediction model is well calibrated and the model prediction probability and observation probability are consistent.the DCA curve indicates that the prediction model has good prediction performance and is suitable for clinical use.Conclusion:1.We found that the probability of positive circumferential resection margin and complications was higher in anterior tumor than in lateral tumor,while there was no significant difference between posterior and lateral tumor,or between anterior and posterior tumor.Anterior wall tumors have a lower long term survival rate.2.Age≥60,CEA≥5ug/L,T stage III/IV,anterior tumor,positive circumferential resection margin,and complications were risk factors for survival after TME for lowgrade rectal cancer.3.The prediction model of survival after laparoscopic TME for low rectal cancer has good accuracy and clinical utility.It can be used as a reference for clinical decision making. |
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