A new lymph node ratio-based staging system for rectosigmoid cancer: a retrospective study with external validation

Abstract

Background: This study evaluated the clinical value of a new AJCC TNM staging prediction model based on lymph node ratio (LNR) in rectosigmoid cancer. Methods: The analysis included 1,444 patients with non-metastatic rectosigmoid cancer diagnosed pathologically between 2010 and 2016 who were collected from the National Cancer Institute Surveillance, Epidemiology, and Results database. The AJCC N-stage was redefined according to the LNR cut-off point, and the ability of the new staging system to predict prognosis was compared with that of the AJCC TNM staging system. Data from 739 patients from our hospital were used for external validation. Results: According to the number of examined lymph nodes and LNR, the N stage was divided into five groups (LNR0-5). The 5-year OS of patients divided according to the new TLNRM staging into stage I (T1LNR1, T1LNR2), IIA (T1LNR3, T2LNR1, T2LNR2, T2LNR3, T1LNR4, T3LNR1), IIB (T2LNR4), IIC (T3LNR2, T4aLNR1, T1LNR5), IIIA (T3LNR3, T2LNR5, T4b LNR1, T4aLNR2, T3LNR4), IIIB (T3LNR5, T4a LNR3, T4a LNR4, T4b LNR2), and IIIC (T4b LNR3, T4a LNR5, T4b LNR4, T4b LNR5) was significantly different (P<0.05). Decision curve analysis showed that the net income of the new TLNRM staging system for different decision thresholds was higher than the prediction line of the traditional 8th TNM staging system. The smaller AIC and BIC suggested that the new staging system had higher sensitivity for predicting prognosis than the traditional staging system. TLNRM Ⅱ and Ⅲ patients benefited from adjuvant chemotherapy, while adjuvant chemotherapy did not improve the prognosis of TNM Ⅱ patients. These findings were confirmed by the external validation data. Conclusion: The new TLNRM staging system was superior to the 8th edition AJCC staging system for staging and predicting the prognosis of patients with rectosigmoid cancer and may become an effective tool in clinical practice.