Intramural and Mesorectal Distal Spread Detected by Whole-Mount Sections in the Determination of Optimal Distal Resection Margin in Patients Undergoing Surgery for Rectosigmoid or Rectal Cancer Without Preoperative Therapy

BACKGROUND: The current Japanese general rules for clinical and pathologic studies on cancer of the colon, rectum, and anus state that a 3-cm distal resection margin is needed in resecting rectosigmoid cancer and rectal cancer with a distal edge above the peritoneal reflection, and 2 cm is needed for rectal cancer with a distal edge below the peritoneal reflection. The appropriateness of these rules has not been proved. OBJECTIVE: Our aim was to evaluate the appropriateness of the Japanese rules. DESIGN AND SETTING: We retrospectively analyzed surgical and pathology records of patients who underwent surgery at a tertiary care cancer center in Japan. PATIENTS: The study included 381 consecutive patients with stage I to IV rectosigmoid or rectal cancer without preoperative chemotherapy or radiotherapy. MAIN OUTCOME MEASURES: We investigated both intramural and mesorectal distal spread, using whole-mount sections to measure the maximum length of distal spread. Long distal spread was defined as distal spread longer than the distal resection margin stated in the Japanese general rules. Risk factors for both distal spread and long distal spread were evaluated. RESULTS: Of 381 patients, 325 (85.3%) had no distal spread and a total of 56 (14.7%) had distal spread. Distal spread was within the limits specified by the Japanese general rules in 48 of the 381 patients (12.6%) and beyond the Japanese limits (long distal spread) in 8 patients (2.1%). The prevalence of distal spread increased with TNM stage (stage I, 2.7%; stage II, 5.3%; stage III, 17.4%; stage IV, 46.2%). Long distal spread was not observed in stage I or II, was found in only 1.4% of patients with stage III disease and in 11.5% of patients with stage IV. The maximum extent of distal spread in patients with rectosigmoid cancer or rectal cancer with the distal edge above the peritoneal reflection was 38 mm; in patients with rectal cancer with the distal edge below the peritoneal reflection, 35 mm. Multivariable analyses showed that nodal involvement and distant metastasis were independent risk factors for distal spread; distant metastasis was the only independent risk factor for long distal spread. CONCLUSIONS: The Japanese general rules specifying the distal resection margin are appropriate for most patients who undergo surgery for rectosigmoid and rectal cancer without preoperative chemotherapy or radiotherapy. A further increase of 1 to 2 cm beyond the recommended distal resection margin may contribute to improved local control for patients with distant metastasis.