Oncologic impact of lateral lymph node metastasis at the distal lateral compartment in locally advanced low rectal cancer after neoadjuvant (chemo)radiotherapy

Introduction: The frequency and oncologic outcomes of lateral lymph node (LLN) metastasis at the most distal lateral compartment (DLC) among clinical stage II-III low rectal cancer patients treated with neoadjuvant (chemo)radiotherapy (nCRT) are poorly understood. The aim was to investigate the oncologic impact of LLN metastasis in the DLC versus the proximal lateral compartment (PLC). Materials and methods: Consecutive patients with low rectal cancer treated with nCRT followed by total mesorectal excision and selective LLN dissection including the DLC were analyzed retrospectively. DLC was defined as the area distal to the infra–piriformis foramen on axial MRI images. Size and location of LLN metastasis on MRI, and survival were retrospectively assessed. Results: Of the 718 patients, 72 (10.0%) had pathological LLN metastasis. Thirty-two (44.4%) had metastasis in the DLC (DLC group), while 40 (55.6%) had metastasis in the PLC without metastasis in the DLC (PLC group). The proportion of ypN2 category tended to be lower in the DLC group (15.6% vs 35.0%, P = 0.105). The median number of metastatic LLN was similar (1 vs. 1, P = 0.691). The median short-axis size of metastatic LLN was smaller in the DLC group than in the PLC group on pre-treatment (P < 0.001) and re-staging (P = 0.004) MRI. By multivariable analysis, LLN metastasis in the DLC was predictive of better disease-free survival (HR, 0.412; 95% CI, 0.159–0.958, P = 0.039). Conclusion: LLN metastasis in the DLC is frequent and has favorable oncologic outcomes after surgical dissection with nCRT.