Rethinking TNM: Tumor deposit-based prognostic models may improve N-staging in colorectal cancer

Introduction

Tumor deposits are an important negative prognostic factor for long-term oncological outcomes in colorectal cancer patients, independent of lymph node status. Several novel models have been proposed to further integrate tumor deposits into the TNM-staging system, but their comparative performance remains unclear. The aim of this study was to identify, compare and validate novel prognostic models incorporating tumor deposits for N-stage classification.

Methods

A scoping literature review identified novel prognostic models that incorporated tumor deposits or tumor deposit count into N-staging. The identified models were validated using patient data from the Swedish Colorectal Cancer Registry, assessing overall survival, distant metastasis, and local recurrence. Prognostic performance was compared to the TNM N-staging using Kaplan-Meier curves for visual analysis, Harrell's C-index for discriminative ability, and Bayesian information criterion for model fit.

Results

Of 792 articles, seventeen met the inclusion criteria, resulting in ten unique models in addition to TNM. For the patient cohort, 26,970 patients remained after exclusion, of whom 3,312 (12 %) had tumor deposits. All models were superior to TNM with two models standing out; an integrated model combining lymph node and tumor deposit count, and a ratio model considering number of tumor deposits, positive lymph nodes, and total number of extracted nodal structures. All models provided prognostic value, but differences were modest.

Conclusion

This study demonstrated that although all models outperformed TNM, prognostic differences between the models were small. While tumor deposits provide valuable prognostic information for high-risk patients, additional risk factors are required to further enhance the staging system.