Cutoff of 25% for Ki67 expression is a good classification tool for prognosis in colorectal cancer in the AJCC‑8 stratification.

Ki‑67 expression has been widely used in clinical practice as an index to evaluate the proliferative activity of tumor cells. The cutoff for Ki67 expression in order to increase the prognostic value of Ki67 expression in colorectal cancer varies. The present study assessed the relationship between the 25% cutoff for Ki67 expression and prognosis in colorectal cancer in the AJCC‑8 (American Joint Committee on Cancer 8 edition) stratification. The current trial included 1,090 colorectal cancer patients enrolled from 2006 to 2012 at Huzhou Central Hospital. Ki67 expression was classified according to 25% intervals, dividing the patients into four groups. Measurement data were analyzed by ANOVA, and count data by Crosstabs. Bivariate correlation analysis was performed to assess clinicopathological indicators based on Ki67 expression. Disease‑free survival (DFS) and overall survival (OS) based on Ki67 levels were analyzed by the Kaplan‑Meier method. A total of 1,090 patients of the 2,080 enrolled CRC cases were evaluated (52.4%). Invasive depth, tumor differentiation, tumor size, AJCC‑8, positive number of lymph nodes and chemotherapy status showed significant differences in the various Ki67 expression groups (all P<0.05), with significant correlations (Spearman rho: 0.170, 0.456, 0.22, 0.195, 0.514 and ‑0.201, respectively, all P<0.001). DFS and OS for the different Ki67 level groups based on AJCC‑8 stratification were analyzed, and no significance was found in stage IV (P=0.334). DFS and OS survival rates were assessed at different Ki67 expression levels, and no significant differences were found (all P>0.05). Cox regression analysis showed that invasive depth, lymph node metastasis, tumor differentiation, AJCC‑8 and Ki67 were independent factors affecting colorectal cancer (P=0.030, all others P<0.001). In conclusion, a cutoff of 25% for Ki67 expression is a good classification tool. High Ki67 has a close association with poor prognosis in colorectal cancer and independently predicts prognosis in the AJCC‑8 stratification.