[Comparison of the anorectal function before and after neoadjuvant radiotherapy in mid-low rectal cancer: a retrospective observational study from single center].

Objective: The aim of this study was to evaluate the impact of neoadjuvant radiotherapy on anorectal function of patients with mid-low rectal cancer by means of high-resolution anorectal manometry. Methods: A retrospective observational study was conducted. Information on patients with mid-low rectal cancer was collected from the prospective registry database of Rectal Cancer at Peking Union Medical College Hospital (PUMCH) from June 2020 to April 2023. Anorectal functions were detected using three-dimensional high-resolution manometry system. Logistic regression analysis was performed to identify the factors associated with the changed anorectal manometry. Results: A total of 45 patients with mid-low rectal cancer were included in the study. Thirty-two (71.1%) patients were male, 13 (28.9%) patients were female. The mean age was 60±11 years, and the mean BMI was 23.4±3.7 kg/m². The mean distance between the lower edge of the tumor and the anal verge was 5.4±1.5 cm. The median size of the tumor was 3.4 (2.9-4.5) cm, and the median circumferential extent of the tumor was 66.0 (45.5-75.0) %. 41 (81.1%) patients were MRI T3-4 and 40 (88.9%) patients were MRI N positive. The resting pressure has a decreasing trend after neoadjuvant radiotherapy (55.3±32.0 mmHg vs. 48.0±28.5 mmHg, t=1.930, P=0.060). There was no significant change in maximum squeezing and the length of the high-pressure zone after neoadjuvant radiotherapy. All volumes describing rectal sensitivity (first sensation, desire to defecate, and maximum tolerance) were lower after neoadjuvant radiotherapy. And maximum tolerance was significantly lower (66.0 [49.0,88.0] ml vs. 52.0 [39.0,73.5] ml, Z=-2.481,P=0.013). Univariate analysis demonstrated that the downstage of N-stage was associated with the decrease in maximum tolerance (OR=6.533, 95%CI:1.254-34.051, P=0.026). Conclusion: Neoadjuvant radiotherapy damages anorectal function by decreasing the resting pressure and rectal sensory threshold of patients. The N-stage downstaging was associated with a decrease in maximum tolerance.