Features of Lateral Pelvic Lymph Nodes Associated With Pathological Involvement After Total Neoadjuvant Therapy in Patients Undergoing Lateral Pelvic Lymph Node Dissection

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 MRI-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 (>= 7mm 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, short-axis lateral node diameter at baseline was <7 mm in 48 patients and >= 7 mm in 59 patients. 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 pretreatment malignant features and posttreatment short-axis diameter >= 4 mm. Five-year relapse-free survival was significantly lower in patients with posttreatment lateral node diameter >= 4mm than those with <4mm (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 pretreatment short-axis diameter <7mm. In patients with pretreatment short-axis diameter >= 7 mm, pretreatment malignant features and posttreatment 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.