Distal Resection Margins Before and After Fixation: A Comparative Analysis in Rectal Cancer Surgery

Background The adequacy of the distal resection margin (DRM) remains a central concern in rectal cancer surgery. However, the interpretation of margin length may be confounded by tissue shrinkage after resection and fixation. Methods We retrospectively reviewed 60 patients who underwent anterior or low anterior resection for rectal cancer between XXXX and XXXX at a single tertiary center. Distal margins were measured intraoperatively on fresh specimens (BF) and remeasured after formalin fixation (AF). Shrinkage was calculated as the percentage change between AF and BF. Demographic variables, surgical procedure, tumor level, and neoadjuvant chemoradiotherapy were analyzed for associations with shrinkage. Results The median age of the cohort was 65,5 years (range: 42–81), and 83% of patients underwent low anterior resection. Neoadjuvant chemoradiotherapy was given to 34 patients (57%). The mean intraoperative DRM was 4,39 cm, while the mean fixed DRM was 3,90 cm, corresponding to an average absolute reduction of 0,49 cm and a mean shrinkage of − 13,2%. Shrinkage ranged from 0% to 70%. Subgroup analyses showed no significant differences according to surgery type, sex, age, or neoadjuvant therapy. Conclusion Formalin fixation leads to measurable shortening of distal margins in rectal cancer specimens. Pathological measurements may underestimate the intraoperative margin, an important consideration particularly in low anterior resections. Surgeons should be mindful of this discrepancy.