Prognostic impact of nodal classification systems in rectal adenocarcinoma: a retrospective cohort study

Lymph node metastasis is a key determinant of prognosis and adjuvant treatment in rectal cancer and is currently staged according to the American Joint Committee on Cancer (AJCC) 8th edition pathological N (pN) classification, which is based solely on the number of metastatic lymph nodes. However, prognostic heterogeneity exists among patients within the same pN category, particularly when lymph node retrieval is inadequate. Alternative nodal metrics, including the lymph node ratio (LNR) and log odds of positive lymph nodes (LODDS), have been proposed to improve risk stratification.

This retrospective study included 170 patients with histologically confirmed rectal adenocarcinoma who underwent curative resection. Cancer-specific survival (CSS) was analyzed using the Kaplan-Meier method, and differences among groups were assessed with the log-rank test. Multivariate Cox proportional hazards models were employed to identify independent prognostic factors. Model performance was evaluated using the area under the curve (AUC), Akaike information criterion (AIC), and chi-square trend and likelihood ratio tests.

All three classification systems-pN, LNR, and LODDS-were significantly associated with CSS (log-rank P<0.001 for all). In multivariable analysis, each nodal classification system was independently associated with CSS after adjustment for covariates. Among them, LNR showed the slightly higher discriminative ability, with the highest AUC at 3 years (0.664), followed by pN (AUC =0.662) and LODDS (AUC =0.603). Prognostic performance improved notably in patients with ≥12 lymph nodes retrieved.

pN, LNR, and LODDS are independent prognostic indicators in rectal cancer. Among them, LNR demonstrates slightly higher prognostic performance and may serve as a more effective tool for risk stratification than the AJCC 8th edition pN classification or LODDS, particularly when lymph node retrieval is adequate.