[Clinical utility of the newly revised AJCC 9th edition colon cancer staging: a single-center retrospective study]

Objective: To evaluate the survival prediction efficacy and clinical value of the newly revised American Joint Committee on Cancer (AJCC) 9th edition colon cancer staging system using a single-center colon cancer database. Methods: This observational study utilized prospectively registered clinical and pathological data of 1222 patients from the colon cancer database of Peking Union Medical College Hospital between January 2016 and February 2022. Inclusion criteria were postoperative pathologically confirmed stage I-III colon adenocarcinoma (according to the AJCC 8th edition) with tumor location ranging from the cecum to the sigmoid colon. Exclusion criteria included multiple primary colorectal cancers, distant organ metastasis detected by preoperative imaging or intraoperative exploration, history of malignancy, neoadjuvant chemoradiotherapy, and endoscopic, local, or palliative resection. Changes in staging between the 8th edition (old version) and the 9th edition (new version) were compared. Survival curves were generated using the Kaplan-Meier method, and differences between curves were assessed using the Log-rank test. The predictive performance of the two models was evaluated using Harrell's concordance index (C-index) and the Akaike Information Criterion (AIC); a lower AIC value and a higher C-index indicated better model discrimination. The linear trend 𝜒² test was used to compare the gradient monotonicity of the two staging models, with a larger 𝜒² value indicating better consistency between staging and survival. Furthermore, univariate and multivariate Cox proportional hazards regression models were used to assess the impact of tumor deposits (TDs) and adjuvant chemotherapy (ACT) on survival outcomes. Results: The cohort included 703 males (57.5%) and 519 females (42.5%), with a median age of 64 (interquartile range: 56, 72) years. According to the new edition, 976 patients (79.9%, 976/1222) experienced a change in stage compared to the old edition, with 714 (58.4%) upstaged and 262 (21.4%) downstaged. The median follow-up was 60.9 (43.3, 77.3) months. In the old edition, the 5-year overall survival (OS) rates for stages I, II, and III were 95.1%, 92.3%, and 77.0%, respectively; the 5-year disease-specific survival (DSS) rates were 97.5%, 96.0%, and 80.9%, respectively. In the new edition, the 5-year OS rates for stages I, II, and III were 96.8%, 93.7%, and 77.9%, respectively; the 5-year DSS rates were 100%, 96.9%, and 81.9%, respectively. The discriminatory power of the new overall staging (I, II, III) was superior to that of the old edition (OS: C-index 0.668 vs. 0.665, AIC 2258.47 vs. 2266.27; DSS: C-index 0.710 vs. 0.709, AIC 1558.80 vs. 1564.33). The linear trend 𝜒² value for the new overall staging was higher than that of the old edition (OS: 57.42 vs. 51.10; DSS: 55.89 vs. 53.82). Within each "overall stage," discrimination between substages decreased, while consistency was higher. The detection of tumor deposits was an independent risk factor for both OS (HR=1.701, 95%CI: 1.178-2.457, P<0.001) and DSS (HR=1.973, 95%CI: 1.303-2.988, P=0.001). For every increment of 1 in the number of tumor deposits, the risk ratio increased by 20.4% for OS (HR=1.204, 95%CI: 1.067-1.359, P=0.003) and 26.6% for DSS (HR=1.266, 95%CI: 1.106-1.449, P<0.001). Under the new staging system, for patients with stage IIIA, the adjuvant chemotherapy group showed better OS (HR=0.342, 95%CI: 0.173-0.675, P=0.002) and DSS (HR=0.276, 95%CI: 0.127-0.598, P=0.001) compared to the non-adjuvant treatment group. For stage IIA patients, adjuvant chemotherapy was not an independent protective factor for OS or DSS. For stage IIB patients, adjuvant chemotherapy was a protective factor for OS but not for DSS. Conclusions: The AJCC 9th edition colon cancer staging system demonstrates superior overall discriminatory power and improved monotonicity of survival curves for stage I-III patients compared to the 8th edition, offering better prognostic consistency. While discrimination between substages within overall stages decreased, internal consistency improved. The detection and increasing number of tumor deposits adversely affect survival. The 9th edition staging system may provide enhanced prognostic value and better guide clinical decision-making regarding treatment strategies.