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.