Association of the transanal approach with the accuracy of distal margin achievement in rectal cancer surgery.

Abstract

Background: Adequate distal margin (DM) achievement is essential in oncological rectal cancer surgery. In conventional transabdominal surgery, however, the intraluminal location of the distal tumor edge must be translated to an externally applied transection line; this potentially causes discrepancies between intended and achieved margins. This study aimed to evaluate the discrepancy between the planned intraoperative DM and the margin achieved in rectal cancer resection, identify factors associated with DM discrepancy, and evaluate the association between the transanal approach, specifically transanal total mesorectal excision, and DM accuracy.

Methods: This retrospective cohort study included 171 consecutive patients who underwent curative-intent laparoscopic or robot-assisted low anterior resection (LAR) or intersphincteric resection between July 2019 and June 2025. The intended DM in operative records was compared with the pathological DM measured in formalin-fixed specimens. The primary outcome was the absolute DM discrepancy. As the distribution was skewed, adjusted median regression was performed using the transanal approach, intended DM, tumor distance from the anal verge, maximum tumor size, surgical platform, and surgical era as covariates.

Results: The median absolute DM discrepancy was 4.0 mm and was smaller with than without the transanal approach (3.0 vs. 6.0 mm; p < 0.001). After adjustment, transanal approach omission was associated with greater absolute DM discrepancy (β, 3.938 mm; 95% confidence interval [CI] 1.848-6.027; p < 0.001). Greater maximum tumor size was also associated with greater discrepancy (β per 1-mm increase, 0.075 mm; 95% CI 0.040-0.110; p < 0.001). This association remained consistent in sensitivity analyses restricted to LAR and after exclusion of scar-based pathological DM measurements.

Conclusions: The transanal approach was associated with a smaller discrepancy between intended and achieved DMs after adjustment for tumor characteristics, surgical platform, and surgical era. Assessing the distal tumor edge and intended transection line within the same transanal operative field may facilitate more precise DM control.