| Summary: | Abstract 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.
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