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Dissection of the lateral lymph nodes with short axis of ≥ 5 mm affects the prognosis in rectal cancer patients: A central review of 738 lower rectal cancer magnetic resonance images.

3578 Background: The usefulness of lateral lymph node dissection (LLND) for lower rectal cancer has been discussed. Concerning relapse-free survival (RFS), in the JCOG0212 trial, the non-inferiority of avoiding LLND for rectal cancer without LLN enlargement of ≥10 mm was not shown; however, the superiority of LLND was also not demonstrated. Methods: To examine whether the difference in dissection effect could be demonstrated by the size of LLN, magnetic resonance imaging (MRI) for the central review of pre-registered patients with stages II/III lower rectal cancer below the peritoneal reflection was performed, and the prognosis of the patients were prospectively investigated as a cohort. The relationship between LLND and RFS was also evaluated. Results: MR images of 738 cases (mean distance from anal verge: 4.5 cm) were evaluated. Twenty patients with LLN enlargement of ≥10 mm were excluded from the analysis. Overall, of 718 patients, 310 did not undergo LLND (non-LLND group), whereas the other 408 underwent LLND (LLND group). The lymph node sizes of ≥5 mm were observed in 10.0% and 21.1% of patients in the non-LLND and LLND groups, respectively. Although there was some bias in the background characteristics of the two groups (non-LLND vs. LLND; median age 66 vs. 61 years; laparoscopic surgery 64.2% vs. 17.9%; preoperative treatment 39.4% vs. 27.9%; circumferential resection margin evaluated by MRI 37.3% vs. 49.9%; and postoperative complications 33.2% vs. 44.4%), almost no difference in the 5-year RFS was observed (63.4% vs. 67.5%).The LLND group had significantly more favorable with ≥5 mm LLN (non-LLND 51.6% vs. LLND 69.0% P = 0.023) than with < 5 mm LLN (non-LLND 64.7%; LLND 67.0%). Conclusions: Oncological benefit of LLND was suggested in patients with enlarged lateral nodes on MRI using a large cohort of clinical stage II/III lower rectal cancer.