Lateral Lymph Node Size and Tumor Distance From Anal Verge Accurately Predict Positive Lateral Pelvic Lymph Nodes in Rectal Cancer: A Multi-Institutional Retrospective Cohort Study

BACKGROUND: Lateral pelvic lymph node dissection improves oncological outcomes in rectal cancer patients with suspected lateral pelvic lymph node metastasis. However, the indication for this procedure remains unclear. OBJECTIVE: This study aimed to identify the predictive factors for lateral lymph node metastasis and the indications for lateral pelvic lymph node dissection. DESIGN: A multi-institutional retrospective study. SETTINGS: This study was conducted at 3 university hospitals. PATIENTS: This study involved 105 patients with locally advanced mid/low rectal cancer and clinically suspected lateral pelvic lymph node metastasis who underwent total mesorectal excision with lateral pelvic lymph node dissection between 2015 and 2020. MAIN OUTCOME MEASURES: Indications were set using lateral pelvic lymph node metastasis-associated preoperative factors. RESULTS: Among 105 patients, 36 (34.3%) had pathologically confirmed lateral pelvic lymph node metastasis and 77 (73.3%) underwent preoperative chemoradiation. Tumors located within 5 cm distance from the anal verge (p = 0.02) and initial node size ≥ 6 mm (p = 0.001) were significant predictors of lateral pelvic lymph node metastasis. The sensitivity was 100% (36/36) with a cutoff of 6 mm for the initial node size and 94.4% (34/36) with a cutoff of 8 mm for the initial node size. When using initial node size cutoffs of 8 mm for anal verge-to-tumor distance of >5 cm and 6 mm for anal verge-to-tumor distance of ≤5 cm, the sensitivity of lateral pelvic lymph node metastasis was found to be 100%. LIMITATIONS: The retrospective design and small sample size were the limitations of this study. CONCLUSION: Initial node size and tumor height were significant predictors of lateral pelvic lymph node metastasis. This study proposed that an initial node size of ≥8 mm with an anal verge-to-tumor distance of >5 cm and ≥6 mm with an anal verge-to-tumor distance of ≤5 cm are optimal indications for lateral pelvic lymph node dissection in rectal cancer.