Effect of Ki-67 Expression Levels and Histological Grade on Breast Cancer Early Relapse in Patients with Different Immunohistochemical-based Subtypes

This retrospective analysis evaluated the interaction between Ki-67 and histological grade and their prognostic role in different breast cancer subtypes. In total, 2,573 breast cancer patients underwent surgery, and their histological grade and Ki-67 values were evaluated by breast pathologists. The median Ki-67 index was 15%, which was used as the cut-off for low/high Ki-67 expression. Recurrence-free survival (RFS) was calculated and compared, and the results indicated that Ki-67 expression was significantly associated with histological grade in all breast cancer patients (p < 0.001) and in each immunohistochemical (IHC)-based subtype (p < 0.001). Both high Ki-67 expression and grade 3 tumours were independent predictors of inferior RFS in all patients, especially in those with luminal-like tumours (p < 0.05). Ki-67 was an independent prognostic factor for RFS in grade 1, 2 patients with luminal-like tumours (adjusted hazard ratio [HR] = 1.92, 95% confidence interval [CI]: 1.22-3.03, p = 0.005), but not in the other subtypes. Similarly, histological grade predicted shorter RFS in patients with low Ki-67 expression who had luminal-like tumours (adjusted HR = 2.12, 95% CI: 1.13-3.99, p = 0.02) but not in the other subtypes. Conversely, Ki-67 showed no prognostic value for patients with grade 3 tumours and vice versa.