BACKGROUND: Radiotherapy with or without chemotherapy has been widely used to improve patient outcomes due to locally advanced rectal cancer. The differential degree of pelvic fibrosis and anorectal function after preoperative or postoperative chemoradiotherapy has not been studied previously. METHODS: Data of patients who received chemoradiotherapy and radical resection of rectal cancer in our hospital from January 2000 to Aug 2021 were retrospectively analyzed. Anastomotic fibrosis scores and perirectal fibrosis scores based on magnetic resonance imaging findings were used to evaluate the extent of fibrosis one year postoperatively. The overall level of anorectal function and percentage of patients eligible for ileostomy reversal were assessed two years postoperatively. RESULTS: 1331 patients were finally included, with 522 and 809 patients in in the preoperative and postoperative chemoradiotherapy groups, respectively. The postoperative chemoradiotherapy group had a higher percentage of patients undergoing ileostomy reversal and had lower anastomotic fibrosis scores, perirectal fibrosis scores, Wexner scores, and percentage of patients with temporary ileostomy than the preoperative group; this difference persisted after propensity score matching. Univariate and multivariate analyses demonstrated that the timing of chemoradiotherapy was an independent predictor of the anastomotic fibrosis score, perirectal fibrosis score, percentage of patients with temporary ileostomy, and percentage of patients eligible for ileostomy reversal. CONCLUSIONS: Postoperative chemoradiotherapy is associated with less pelvic fibrosis and better anorectal function than preoperative chemoradiotherapy in the treatment of patients with locally advanced rectal cancer.

The authors have declared no competing interest.

This study did not receive any funding

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Ethics Committee of Shanghai Changhai Hospital gave ethical approval for this work.

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