Ki67 Labeling Index Predicts Poor Long-term Relapse-free Survival in Patients with Invasive Stage I-II Breast Cancer After Breast-conserving Therapy

[Abstract] Background: The purpose of this retrospective study was to investigate the predictive ability of the Ki67 labeling index (LI) for relapse-free survival (RFS) of patients with stage I-II invasive breast cancer after breast-conserving therapy. Materials and methods: Between 2012 and 2016, 240 patients with stage I-II invasive breast cancer were treated at our hospital with breast-conserving therapy. Survival outcomes were analyzed using the Kaplan-Meier and cumulative incidence methods. Factors including T stage, N stage, estrogen receptor, HER2, and Ki67 LI were evaluated with regard to RFS using Cox proportional hazard regression. Results: The median duration of follow-up in the surviving patients was 36 months (range, 14-62 months). Rates of 3-year overall survival and RFS were 98.1% and 96.4%, respectively. Three-year cumulative rates of local recurrence, regional recurrence, and distant metastasis were 1.3%, 1.2%, and 2.1%, respectively. Multivariate analysis revealed that a Ki67 LI >=33.3% was the only prognostic factor for RFS. Conclusion: A Ki67 LI >=33.3% was a predictor of significantly worse RFS.