Oncological Impact of Lateral Lymph Node Dissection After Preoperative Chemoradiotherapy in Patients with Rectal Cancer

Purpose: To evaluate the efficacy of selective lateral lymph node dissection (LLND) and the effect of preoperative chemoradiotherapy (PCRT) in patients with LLN ≥ 5 mm. Methods: Patients who underwent PCRT for rectal cancer were classified: (A) total mesorectal excision (TME)-only with LLN < 5 mm (2001–2009, n = 474), (B) TME-only with LLN < 5 mm (2011–2016, n = 273), (C) TME-only with LLN ≥ 5 mm (2001–2009, n = 102), and (D) TME-LLND with LLN ≥ 5 mm (2011–2016, n = 69). Subgroup analysis was performed in patients with LLN ≥ 5 mm based on the reduction in LLN size to < 5 mm or not on restaging MRI after PCRT. Results: Oncological outcomes did not differ between groups A and B. Group D had lower 3-year local recurrence (LR) (20.13% vs 5.39%, P = 0.0013) and higher relapse-free survival (RFS) (65.83% vs 77.11%, P = 0.0436) than group C, while the 3-year overall survival (OS) was not significantly different between the two groups (87.64% vs 93.53%, P = 0.0670). In patients with reduction of LLN size from ≥ 5 mm to < 5 mm, LLND significantly reduced LR than did TME alone, but there were no significant differences in survival outcomes. In patients without reduction of LLN size to < 5 mm, LLND reduced LR and improved RFS compared with TME alone. Conclusions: Selective LLND reduced LR and improved RFS in patients with LLN ≥ 5 mm. Selective LLND reduced LR in patients with reduction of LLN size from ≥ 5 mm to < 5 mm after PCRT, and improved both LR and RFS in patients without reduction of LLN size to < 5 mm.