QS110 - Is Lateral Pelvic Lymph Node Dissection Necessary for Good Responders After Neoadjuvant Chemoradiation in Rectal Cancer?

Purpose/Background: Selective lateral pelvic lymph node dissection (LPND) is recommended in patients with clinically suspected lateral pelvic lymph node (LPN) metastasis. However, the role of LPND is still unclear in patients with good response to the preoperative chemoradiation (CRT). The aim of this study is to identify the optimal treatment strategy in rectal cancer patients with good response to the preoperative CRT.

Methods/Interventions: This study involved a chart review of patients with locally advanced rectal cancer and clinically suspected LPN metastasis, who underwent preoperative CRT followed by total mesorectal excision with LPND. The study included patients from three hospitals affiliated with The Catholic University of Korea who were treated between January 2016 and November 2022. The patients were divided into two groups, good and poor responders, based on the size cut-offs of 5mm which was the short axis diameter of the largest LPN on magnetic resonance imaging after CRT. Risk factors for LPN metastasis were assessed in good and poor responder groups, respectively.

Results/Outcomes: A total of 91 patients were included. Among them, good and poor responses to preoperative CRT were observed in 38 (41.8%) and 53 (58.2%) patients, respectively. LPN sizes were larger in poor responder than in good responder before and after CRT, respectively (11.5±5.2 vs. 7.1±2.5, p< 0.001 and 8.6±4.6 vs. 3.3±1.6, p< 0.001). LPN metastasis was significantly more observed in poor responder (18 patients, 34.0%) than in good responder group (5 patients, 13.2%) (p=0.024). Multivariate analysis revealed tumor location within 5cm from anal verge (AV) [odds ratio (OR) 4.74, 95% confidence interval (CI) 1.66-13.55] and poor response to preoperative CRT [OR 3.35, 95% CI 1.06-10.58] were independent risk factor for LPN metastasis. In good responder group, tumors were located within 5cm from AV in all five patients with LPN metastasis. Low rectal cancer (AV≤ 5cm) was only significant predictive factor for LPN metastasis in good responder group (p=0.004). On the other hand, LPN sizes before and after CRT were not predictive factor for LPN metastasis (p=0.947 and 0.910). In poor responder group, initial LPN size (14.19±7.1 vs. 10.12±3.2, p=0.006) and post CRT LPN size (11.11±7.0 vs. 7.27±1.6, p=0.033) were significant risk factors for LPN metastasis. When the indications for LPND were set as all poor responders and good responders with tumor within 5cm from AV, the sensitivity for diagnosis of LPN metastasis was 100%. Using this criterion, 63.2% of the patients could be spared LPND in good responder group.

Conclusion/Discussion: Pathological lateral pelvic lymph node metastasis was observed even in 13.2% of good responder after preoperative CRT and tumor location was a significant risk factor for LPN metastasis in good responder. Therefore, LPND should be considered in the patients with low rectal cancer (AV≤ 5cm), even if a good response to the preoperative CRT was obtained.