Objective:To investigate clinical efficacy of conformal sphincter preservation operation (CSPO) versus intersphincteric resection (ISR) in the treatment of low rectal cancer.Methods:The retrospective cohort study was conducted. The clinicopathological data of 183 patients with low rectal cancer who were admitted to two medical centers (117 in the Changhai Hospital of Naval Medical University and 66 in the Huashan Hospital of Fudan University) from August 2011 to April 2020 were collected. There were 110 males and 73 females, aged (57±11)years. Of 183 patients, 117 cases undergoing CSPO were allocated into CSPO group, and 66 cases undergoing ISR were allocated into ISR group, respectively. Observation indicators: (1) surgical situations of patients with low rectal cancer in the two groups; (2) postoperative complications of patients with low rectal cancer in the two groups; (3) follow-up; (4) influencing factors for prognosis of patients with low rectal cancer; (5) influencing factors for satisfaction with the anal function of patients with low rectal cancer. Follow-up was conducted using outpatient examination, questionnaire and telephone interview to determine local recurrence, distal metastasis, survival, stomal closure, satisfaction with the anal function of patients. Measurement data with normal distribution were represented as Mean±SD, and comparison between groups was analyzed using the t test. Measurement data with skewed distribution were represented as M (range). Count data were described as absolute numbers or percentages, and comparison between groups was analyzed using the chi-square test. Comparison of ordinal data was analyzed using the rank sum test.The Kaplan-Meier method was used to draw survival curves, and life table method was used to calculate survival rates. Log-rank test was used for survival analysis. Univariate analysis was performed using the linear regression. Variables with P<0.10 in the univariate linear regression analysis were included for multivariate analysis. Multivariate analysis was performed using the COX stepwise regression model and linear regression analysis. Results:(1) Surgical situations of patients with low rectal cancer in the two groups: cases with laparoscopic surgery, operation time, volume of intraoperative blood loss, distance from tumor to distal margin, cases with postoperative chemotherapy, duration of postoperative hospital stay were 44, (165±54)minutes, (142±101)mL, (0.6±0.4)cm, 76, (6.6±2.5)days for the CSPO group, respectively, versus 55, (268±101)minutes, (91±85)mL, (1.9±0.6)cm, 9, (7.9±4.7)days for the ISR group, showing significant differences between the two groups ( χ2=35.531, t=8.995, -3.437, -3.088, χ2=44.681, t=2.267, P<0.05). (2) Postoperative complications of patients with low rectal cancer in the two groups: 19 patients in the CSPO group had complications. There were 6 cases with grade Ⅰ complications, 12 cases with grade Ⅱ complications, 1 case with grade Ⅲb complication. Fourteen patients in the ISR group had complications. There were 4 cases with grade Ⅰ complications, 7 cases with grade Ⅱ complications, 1 case with grade Ⅲa complication, 2 cases with grade Ⅲb complications. There was no significant difference in the postoperative complications between the two groups ( χ2=0.706, P>0.05). Patients with complications in the two groups were improved after symptomatic and supportive treatment. There was no perioperative death in the postoperative 30 days of the two groups. (3) Follow-up: 183 patients received follow-up. Patients of the CSPO group and ISR group were followed up for (41±27)months and (37±19)months, respectively, showing no significant difference between the two groups ( t=-1.104, P>0.05). There were 2 cases with local recurrence and 9 cases with distal metastasis of the CSPO group, respectively, versus 3 cases and 4 cases of the ISR group, showing no significant difference between the two groups ( χ2=1.277, 0.170, P>0.05). The 3-year disease-free survival rate and 3-year total survival rate were 84.0% and 99.0% for the CSPO group, versus 88.6% and 92.8% for the ISR group, showing no significant difference between the two groups ( χ2=0.218, 0.002, P>0.05). The stomal closure rate was 92.16%(94/102) and 96.97%(64/66) for 102 patients of CSPO group and 66 patients of ISR group up to postoperative 12 months,respectively, showing no significant difference between the two groups ( χ2=1.658, P>0.05). Of the 8 cases without stomal closure in the CSPO group, 2 cases refused due to advanced age, 4 cases subjectively refused, and 2 cases were irreducible due to scar caused by radiotherapy. Two cases in the ISR group had no stomal closure including 1 case of postoperative liver metastasis and 1 case of subjective refusal. There were 92 and 61 patients followed up to 12 months after stomal closure, of which 75 cases and 38 cases completed questionnaires of satisfaction with the anal function. The satisfaction score with the anal function was 6.8±2.8 and 5.4±3.0 for CSPO group and ISR group, respectively, showing a significant difference between the two groups ( t=-2.542, P<0.05). Fifty-four cases in the CSPO group and 21 cases in the ISR group had satisfaction score with the anal function >5, showing no significant difference between the two groups ( χ2=3.165, P>0.05). (4) Influencing factors for prognosis of patients with low rectal cancer: results of COX stepwise regression analysis showed that gender and pT staging were independent influencing factors for disease-free survival rate of patients with low rectal cancer ( hazard ratio=2.883, 1.963, 95% confidence interval as 1.090 to 7.622, 1.129 to 3.413, P<0.05). Gender and pT staging were independent influencing factors for total survival rate of patients with low rectal cancer ( hazard ratio=10.963,3.187, 95% confidence interval as 1.292 to 93.063, 1.240 to 8.188, P<0.05). (5) Influencing factors for satisfaction with the anal function of patients with low rectal cancer: results of univariate analysis showed that surgical method and tumor differentiation degree were related factors for satisfaction with the anal function of patients with low rectal cancer (partial regression coefficient=1.464, -1.580, 95% confidence interval as 0.323 to 2.605, -2.950 to -0.209, P<0.05). Results of multivariate analysis showed that surgical method, tumor differentiation degree and preoperative radiotherapy were independent influencing factors for satisfaction with the anal function of patients with low rectal cancer (partial regression coefficient=1.637, -1.456, -1.668, 95% confidence interval as 0.485 to 2.788, -2.796 to -0.116, -2.888 to -0.447, P<0.05). Conclusion:Compared with ISR, CSPO can safely preserve the anus in the treatment of low rectal cancer, without increasing the incidence of postoperative complications, which can also guarantee the oncological safety and improve the postoperative anal function.