Distal Bowel Surgical Margin Shorter than 1 cm After Preoperative Radiation for Rectal Cancer: Is It Safe?

Background: The primary end-point of our randomized trial was sphincter preservation. The secondary aim was to evaluate whether distal bowel clearance <= 1 cm is safe after radiation. Methods: The study randomized 312 patients with cT3-4 resectable low-lying and mid-rectal cancer to receive either preoperative irradiation (5 x 5 Gy) with immediate total mesorectal excision (TME) or chemoradiation (50.4 Gy, bolus 5-fluorouracil and leucovorin) with delayed TME. After anterior resection, pathologists prospectively measured macroscopic and microscopic distal bowel clearance. Results: Macroscopic and microscopic distal bowel clearance, distal intramural spread, sphincter preservation, local control, disease-free survival, and overall survival did not differ in the two randomized groups. Pooled analysis of the two groups showed that the incidence of local recurrence at 4 years (median follow-up) for patients with macroscopic clearance <= 1 cm (n = 42) and > 1 cm (n = 124) was 11.3% and 15.4%, respectively (P = 0.514); the hazard ratio (HR) was 0.70, and the 95% confidence interval (CI) was 0.23-2.07. The corresponding values for patients with microscopic clearance <= 1 cm (n = 51) and > 1 cm (n = 101) were 9.6% and 17.6% (P = 0.220; HR 0.51; 95% CI 0.17-1.53). Conclusion: After preoperative radiotherapy, distal bowel clearance <= 1 cm did not compromise local control.