Lateral lymph node metastasis without mesenteric lymph node involvement in middle-low rectal cancer: Results of a multicentre lateral node collaborative group study in China

Background: Characteristics and prognoses of lateral lymph node (LLN) metastasis but not mesenteric lymph node (LN) metastasis are poorly understood. This study explored patterns of mesenteric and LLN metastases in rectal cancer patients. Method: This retrospective, multicentre study was conducted at three institutions and included patients who underwent total mesorectal excision (TME) with lateral lymph node dissection (LLND) for rectal cancer (n = 271). Results: Among the patients with LLN metastases, 210 patients (77.5 %) with clinical stage T3-4 disease and 157 patients (57.9 %) with clinical stage N1-N2 disease underwent TME as well as LLND. The prognoses of patients with metastasis confined to LLNs were significantly better than those of patients with both mesenteric and LLN metastases (3-year overall survival: 85.0% vs. 51.0 %, p = 0.005; 3-year disease-free survival: 75.0% vs. 26.5%, p = 0.003) and were similar to those of patients with metastasis confined to mesenteric LNs (3-year overall survival: 85.0 % vs. 83.8 %, p = 0.607; 3-year disease-free survival 75.0 % vs. 68.8 %, p = 0.717). Patients with metastases confined to LLN had a lower proportion of poor histological types (20.0 % vs. 65.3 %, p = 0.002), lymphatic invasion (20.0% vs. 59.2 %, p = 0.036) and number of LLN metastases (1.6 vs 2.7, p = 0.004), and all metastases were confined to the internal iliac or obturator region (100.0 % vs. 77.6 %, p = 0.008) compared to patients with both mesenteric and LLN metastasis. Conclusions: Approximately a quarter of patients with rectal cancer have LLN metastases but no mesenteric LN metastases. These patients have favourable pathological features and prognoses and can be managed and treated for mesenteric LN metastasis.