A New N Staging System for Colorectal Cancer in the Era of Extended Lymphadenectomy.

BACKGROUND: Complete mesocolic excision is becoming popular in colon cancer surgery in Western countries, and in the tumor-node-metastasis (TNM) classification of rectal cancer, a part of the lateral pelvic lymph nodes is classified as regional. However, the appropriateness of TNM staging according to the assessment of nodal status exclusively by extended lymphadenectomy remains unclear.

PATIENTS AND METHODS: Using a nationwide multicenter database in Japan, we retrospectively analyzed 6866 patients with stage III colorectal cancer (CRC) treated with extended (D3) dissection. First, the best cutoff values for the number of metastatic nodes were explored. Second, the utility of the metastatic status of the main lymph nodes (i.e., at the origin of the feeding artery) and the lateral pelvic lymph nodes ("jN3" category in the Japanese staging system) as N staging criteria was evaluated. The modified N staging system that had the best risk stratification power was determined according to the Akaike information criterion (AIC).

RESULTS: Excellent performance was noted when the number of metastatic nodes was categorized by cutoff values of "3/4" and "6/7." Categorization of nodal metastasis was proven the most clinically efficacious when classified as modified-N1 (N1 and jN3-negative), modified-N2a (N2a and jN3-negative), and modified-N2b (N2b and/or jN3-positive; AIC, 22,810.8), rather than the classification based on the TNM (AIC, 22,849.2) or Japanese staging system (AIC, 22,811.1).

CONCLUSIONS: We structured a modified N staging system according to the number and extent of lymph node metastases. The modified system may be used in stage III cases for precise risk stratification.