The Significance of Lateral Lymph Node Metastasis in Low Rectal Cancer: a Propensity Score Matching Study

Background The indications for lateral lymph node dissection (LLND) in rectal cancer have been controversial. The purpose of this study was to clarify the significance of lateral lymph node metastasis in low rectal cancer. Methods This was a retrospective study at a high-volume cancer center in Japan. In this study, 40 patients with pathologically positive LLN (LLN+) were matched with 175 negative (LLN-) patients by propensity score matching (PSM). COX regression analysis was used to identify independent risk factors related to prognosis. The relapse-free survival rate (RFS) and overall survival rate (OS) of the 2 groups before and after matching were analyzed. Results Of the 64 patients undergoing LLND, 40 (62.5%) patients had LLN+ disease. The LLN+ patients showed deeper infiltration of the primary tumor than the LLN- patients (T3-T4: 87.5% vs. 72.0%; p = 0.044), a greater number of metastatic lymph nodes (N2: 75.0% vs. 35.4%; p < 0.001), and a higher rate of local recurrence (30% vs. 9.1%; p < 0.001). Adjuvant chemotherapy was more common in the 40 LLN+ patients than in the 175 LLN- patients (70.0% vs. 46.8%; p = 0.008). After relapse, the rate of first-line chemotherapy administration for LLN+ patients was higher than that for the LLN- patients (62.5% vs. 29.5%; p = 0.005). The RFS of LLN+ patients was shorter than that of the LLN- patients (p = 0.005). After PSM, although more LLN+ patients received adjuvant chemotherapy than the LLN- patients (70.0% vs. 40.0%; p = 0.007), the local recurrence rate remained higher (30% vs. 10%; p = 0.025). The differences between RFS (p = 0.655) and OS rates (p = 0.164) of the 2 patient groups were not significant. Conclusion Even after LLND, patients with LLN+ low rectal cancer still showed an elevated local recurrence rate. Controlling local recurrence by adjuvant chemotherapy alone is difficult, and the additional strategic treatments are needed.