Proposal of a modified subclassification system for stage III colorectal cancer: A multi-institutional retrospective analysis

Aim: The prognostic value of the stage III subclassification system based on the Japanese Classification of Colorectal, Appendiceal, and Anal Carcinoma has not yet been clarified. This study aimed to develop a modified system with optimal risk stratification and compare its performance with the current staging systems. Methods: Clinicopathological data from 6855 patients with stage III colorectal cancers who underwent D3 dissection were collected from a nationwide multicenter database. After determining patient survival rates across 13 divisions based on pathological N stage (N1, N2a, and N2b/N3) and tumor depth (T1, T2, T3, T4a, and T4b), except for T1N2a and T1N2b/N3 due to the small number, we categorized patients into three groups and developed a trisection staging system according to the Akaike information criterion. We then compared the Akaike information criterion of the developed system with those of the current staging systems. Results: The T1N1_{[rank, 1]} division (98.5%) had the most favorable prognosis in terms of 5-year cancer-specific survival, followed by T2N1_[2] (93.9%), T2N2a_[3] (92.0%), T3N1_[4] (87.0%), T3N2a_[5] (78.8%), T4aN1_[6] (78.7%), T2N2b/N3_[7] (77.8%), T4aN2a_[8] (75.2%), T4bN1_[9] (73.5%), T3N2b/N3_[10] (64.7%), T4aN2b/N3_[11] (61.5%), T4bN2b/N3_[12] (43.0%), and T4bN2a_[13] (42.5%). Compared to the categorizations of the Japanese and tumor-node-metastasis systems (Akaike information criterion, 22 684.6 and 22 727.1, respectively), the following stage categorizations were proven to be the most clinically efficacious: T1N1_[1]-T3N1_[4], T3N2a_[5]-T4bN1_[9], and T3N2b/N3_[10]-T4bN2a_[13] (Akaike information criterion, 22 649.2). Conclusion: The proposed modified system may be useful in the risk stratification of patients with stage III colorectal cancer who had undergone D3 dissection.