Prognostic value of the number of retrieved lymph node and lymph node ratio in locally advanced rectal cancer after preoperative radiation therapy.

582 Background: To assess the prognostic impact of total number of retrieved lymph node (TNN) and lymph node radio (LNR) in patients with locally advanced rectal cancer who received preoperative radiation therapy and surgery Methods: We retrospectively analyzed data from 677 patients with locally advanced rectal cancer who underwent preoperative radiation therapy followed by mesorectal excision at Asan Medical Center between October 1999 and May 2009. The median radiation dose was 50 Gy, and 674 patients (99%) underwent concurrent chemotherapy. All patients were divided into two groups according to the status of lymph node involvement. We assessed the influence of TNN on overall survival (OS) and disease-free survival (DFS) in the patients with node-negative disease (pN0, n = 490), and the prognostic value of LNR, estimated by dividing the number of positive nodes by the number of lymph nodes examined, in the patients with node-positive disease (pN1-2, n = 187). Results: The median follow-up period was 74 months.Patients with pN0 had median 12 lymph nodes examined (range, 0-38). Comparing with patients who had ≤ 8 TNN, patients with > 9 TNN had significantly higher 5-year OS (89% vs. 95%, p = 0.038) and DFS rates (81% vs. 90%, p = 0.013). Multivariate analysis showed that TNN more than 9 was significant prognostic factor for OS (p = 0.032) and DFS (p = 0.007). For patients with pN1-2, patients with low LNR (≤ 0.33, n = 144) showed significantly higher 5-year OS (33% vs. 73%, p < 0.001) and DFS rates (18% vs. 56%, p < 0.001) than high LNR group (> 0.33, n = 43). Also, low LNR was independent prognostic factor for OS (p = 0.001) and DFS (p < 0.001) in multivariate analysis. Conclusions: TNN for node-negative rectal cancer and LNR for node-positive rectal cancer are independent prognostic factors for survival outcome in patients with locally advanced rectal cancer after preoperative radiation therapy. These factors could be considered as useful prognostic indicators irrespective of current TNM staging system.