BACKGROUND: There is a lack of consensus regarding treating involved lateral pelvic lymph nodes in rectal cancer. OBJECTIVE: This study aimed to evaluate the clinical and magnetic resonance imaging-based factors associated with pathological lateral pelvic lymph node metastasis in patients undergoing total neoadjuvant therapy and lateral pelvic lymph node dissection. DESIGN: This is a retrospective study. SETTINGS: This study was conducted at a single comprehensive cancer center. PATIENTS: A total of 107 patients with advanced low rectal cancer with pretreatment enlarged lateral pelvic lymph nodes (≥7 mm in long-axis) undergoing total neoadjuvant therapy with long-course chemoradiotherapy, followed by total mesorectal excision and lateral pelvic lymph node dissection, were enrolled. MAIN OUTCOME MEASURES: Pathological lateral pelvic lymph node metastasis and survival. RESULTS: Among 107 patients, 48 had a short-axis lateral node diameter <7 mm at baseline, while 59 had ≥7 mm. The ≥7 mm group showed significantly higher rates of pathological lateral pelvic lymph node metastasis (44.1% vs. 2.1%; p < 0.0001). In this group, pathological lateral pelvic lymph node metastasis was independently associated with pre-treatment malignant features and post-treatment short-axis diameter ≥4 mm. Five-year relapse-free survival was significantly lower in patients with post-treatment lateral node diameter ≥ 4 mm than those with <4 mm (71.1% vs. 86.2%, p = 0.0364). Patients with pathological lateral pelvic lymph node metastasis had significantly lower overall survival, relapse-free survival, and local recurrence-free survival rates. LIMITATIONS: Selection bias exists in a retrospective analysis. CONCLUSIONS: Pathological lateral pelvic lymph node metastasis is rare in patients with pre-treatment short-axis diameter <7 mm. In patients with pre-treatment short-axis diameter ≥7 mm, pre-treatment malignant features and post-treatment short-axis diameter are both associated with pathological lateral pelvic lymph node metastasis. These factors should be considered when deciding whether to proceed with lateral pelvic lymph node dissection after total neoadjuvant therapy. See Video Abstract.
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