Four risk parameters, established and validated by our previous study to be independent risk factors for predicting BCSS in pN0-1 breast cancer patients receiving mastectomy, namely, age (≤40 versus >40 years old), number of positive lymph nodes (1–2 versus 3 positive lymph nodes), T stage (T1 versus T2), and Ki67 index (≤20% versus >20%), were utilized to divide patients into a low-risk group, which was defined as patients with no or one risk factor, and a high-risk group, which was defined as patients with two or more risk factors. The gene discussed is MKI67; the disease is breast cancer.