A Critical Examination of the Changes Proposed by the AJCCCCEP for the AJCC 9th Edition Colorectal Cancer Staging System

The AJCC 8th edition colorectal cancer (CRC) staging system demonstrates non-hierarchical survival outcomes, with stage IIIA survivals consistently approximating stage I and exceeding stage II. The AJCC Colon Cancer Expert Panel (AJCCCCEP) has attempted to address this with its new proposal for the 9th edition, which incorporates tumor deposits (TDs) as an independent parameter and rebalances the relative significances of the T-stages and N-stages. We sought to critically assess these proposals in a large single-centre cohort. Patients undergoing CRC resection at our institution from 2005 to 2024 were staged according to the proposed system. Overall survival (OS) was evaluated using Kaplan-Meier analysis and pairwise comparisons made through log-rank tests (P < 0.05). Four thousand two hundred fifty-seven CRC patients were identified (median age 74 y, 51% female; 36% node-positive, 17.5% TD positive). Median duration of follow-up was 8.5 years. The proposed staging produced hierarchical OS separation, and all pairwise comparisons achieved statistical significance except stage I versus IIA (P=0.5), I versus IIB (P=0.081), and IIA versus IIB (P=0.10). Surprisingly, in subgroup analysis, patients with low T-stage (T1/T2) with lymph node metastases or tumor deposits (who comprised a small component of the proposed stage IIB grouping) demonstrated superior survival compared with T1/T2 node and tumor deposit-negative patients (P=0.014). We conclude that the changes proposed by the AJCCCCEP for the 9th edition are an improvement and achieve hierarchical survival stratification. However, if our findings are confirmed in other independent cohorts, the proposal's application in T1/T2 stage disease may need refinement.