What is the impact of systemic chemotherapy for lateral lymph nodes in patients with locally advanced low rectal cancer?

Purpose Systemic chemotherapy (SC) before surgery is a potential treatment to improve survival in patients with advanced rectal cancer. However, the impact of SC on lateral lymph nodes (LLNs) remains unclear. Methods A total of 78 patients with stage II/III low rectal cancer, who received 3-month oxaliplatin-based SC followed by LLN dissection (LLND) in principle, were analysed retrospectively. "Total lateral lymph node metastases (tLLNMs)" was defined as having either pathological LLNMs (pLLNMs) or lateral local recurrences (LLRs). Patients with the maximum short-axis size of LLNs >= 7 mm were classified into the swollen group (n = 21). Results In the total cohort, tLLNMs included 6 pLLNMs (7.7%) and 2 LLRs (2.6%). In the non-swollen group, no patients had pLLNMs, but one had LLR (1.8%). In the swollen group, pLLNMs and LLRs were detected in 6 (28.6%) and 1 (4.8%), respectively. The swollen group was an independent risk factor for tLLNMs (P < 0.001), leading to the significantly worse 5-year relapse-free survival (RFS) of 52.4% than the others. Conclusion For patients without swollen LLNs, SC could allow for omission both of lateral irradiation and LLND. For patients with swollen LLNs, the lateral local control was favourable after SC and LLND without chemoradiotherapy (CRT); however, oxaliplatin-based SC might be insufficient to improve survival, requiring more intensive chemotherapy. CRT should be indicated according to the other risk factors of central local recurrence, although the swollen LLNs should be removed.