To identify the prognostic and clinical application values of tumor size in patients with stage II colorectal cancer (CRC).

The clinicopathological characteristics of patients with stage II CRC treated in the Sixth Hospital of Sun Yat-sen University from October 2007 to March 2020 were retrospectively analyzed. Patients were divided into high-risk and low-risk groups in terms of the high-risk factors reported in guidelines. Kaplan-Meier method was used to draw survival curves, and log-rank test was used to compare survival differences. The independent risk factors affected the prognosis of patients with stage II CRC were determined through univariable and multivariable Cox regression analyses. Based on the results of multivariate Cox regression analysis, a nomogram was constructed.

A total of 3 114 patients were included in the study, including 1 149 patients in the high-risk group and 1 965 patients in the low-risk group. Only in the low-risk group, relative to the patients with a tumor size ＞ 5 cm, the patients with a tumor size ≤ 5 cm had significantly poorer 5-year disease-free survival rate (DFS) (83.1% vs. 89.8%, χ2=6.004,P=0.014). Multivariable Cox regression analysis showed that tumor size ≤ 5 cm, age ＞ 60 years, CEA ＞ 5 ng/mL, CA125 ＞ 35 U/mL and postoperative complications were independent prognostic risk factors for patients in the low-risk group. Based on the above five factors, a nomogram for low-risk group was constructed. The model was evaluated by concordance index (0.663), areas under the receiver operating characteristic curve (0.796 for 1-year, 0.760 for 3-year and 0.654 for 5-year) and calibration curves fitted well with reference line, which showed the model had good performance.

Tumor size is an independent prognostic factor for patients with stage II low-risk CRC, but not for patients with stage II high-risk colorectal cancer. The nomogram constructed in the study can accurately predict the 1-, 3-, and 5-year disease-free survival rates of patients with stage II low-risk CRC.