Bowel function after sphincter-preserving treatment with neoadjuvant therapy for low rectal cancer.

3665 Background: Neoadjuvant therapy (NAT) is important for locally advanced rectal cancer, including neoadjuvant chemoradiotherapy (nCRT) and neoadjuvant chemotherapy alone (nCT). Based on the tumor response, sphincter-preserving treatment such as low anterior resection (LAR) or watch and wait (WW) strategy can be implemented. The effects of these therapy combinations on functional outcomes for low rectal cancer remain unclear. Methods: We conducted a retrospective study recruiting patients who were treated at The Sixth Affiliated Hospital of Sun Yat-sen University between 2010 and 2023. Patients who underwent sphincter-preserving treatment after NAT for low rectal cancer with no distant metastasis were eligible. Low rectal cancer was defined as the tumor height no more than 5 cm from the anal verge. Patients with multiple primary carcinoma or familial adenomatous polyposis were excluded. The incidence of low anterior resection syndrome (LARS) was assessed using the LARS score. Oncological outcomes included overall survival (OS), disease-free survival (DFS), and stoma-free survival (SFS). Functional and oncological outcomes were evaluated based on Wilcoxon signed-rank test and Kaplan-Meier survival analysis. The difference of baseline characteristics in different treatment groups was analyzed using propensity scores with inverse probability treatment weighting (IPTW). Results: We enrolled 590 patients: 49 in nCRT+WW group, 181 in nCT+LAR group and 360 in nCRT+LAR group. Median follow-up was 3.4 years (IQR 2.8-4.4), 5 years (IQR 4.3-7.1) and 7.3 years (IQR 4.8-9.3), respectively. After IPTW, all baseline characteristics were similar in the three groups. 3-year OS was 91.0% (95% CI 81.6-100.0) for nCRT+WW group, 89.3% (84.5-94.5) for nCT+LAR group, 93.2% (90.7-95.7) for nCRT+LAR group. 3-year DFS was 62.5% (95% CI 45.6-85.7), 71.0% (64.1-78.6) and 77.5% (77.3-81.9), respectively. There was no differences in oncological outcomes. The incidence of major LARS in the three groups was 0% (0/18.6), 34.1% (35.2/103.2) and 45.9% (104.2/226.8). 3-year SFS without IPTW was 95.2% (20/21) for nCRT+WW, 91.0% (152/167) for nCT+LAR, and 79.7% (244/306) for nCRT+LAR. Conclusions: This retrospective study shows similar oncological outcomes in the three sphincter-preserving strategies for low rectal cancer, while nCRT+WW presented with superior bowel function. Functional outcomes are inversely correlated to the intensity of local therapy. Outcomes for the three therapy combinations after IPTW. nCRT+WW nCT+LAR nCRT+LAR Tumor Height, cm 2.71 (1.20) 3.74 (0.83) 3.60 (0.91) Clinical Stage III, % 75.4 69.1 70.3 3-year OS, % 91.0 89.3 93.2 3-year DFS, % 62.5 71.0 77.5 Major LARS, % 0 34.1 45.9 Minor LARS, % 22.5 22.9 24.1 None LARS, % 77.5 43.0 30.0 3-year SFS*, % 95.2 91.0 79.7 *Without IPTW.