Abstract: Background and purpose: Tumor budding is a poor prognostic factor in colorectal cancer. In this study, we studied the tumor budding by counting the actual number in 10 high power fields and evaluated its clinical application in predicting lymph node metastasis of T₁ colorectal cancer. Methods: Tissue specimens from 307 patients with histologically confirmed T1 colorectal cancer were enrolled. The clinicopathological characteristics including tumor budding were evaluated for their predictive value in lymph node metastasis. A formula was created to calculate the risk score for prediction of lymph node metastasis which was validated by 14 new cases. Results: In the multivariate analysis, it showed that tumor grade, lymphovascular invasion and the number of tumor budding were significantly associated with lymph node metastasis. The probability of lymph node metastasis was calculated using the following equations: Z=1.571×(lymphovascular state: invasion, 1; no invasion, 0)+2.661×(tumor grade: high grade, 1; low grade, 0)+0.024×(budding counts)−3.885; Probability=1/1+e^−Z. The high scores were correlated with the lymph node metastasis in the validations. Conclusion: We can accurately assess the risk of lymph node metastasis by counting the number of tumor budding in 10 high power fields. Therefore tumor budding could potentially assist treatment decision making in T₁ colorectal cancer patients with high-risk lymph node metastasis.

Key words: Tumor budding, Lymph node metastasis, Colorectal cancer, Risk score