Distant disease-free survival according to Ki-67 and progesterone receptor expression levels. (a) Patients with low Ki-67 levels (<14%). (b) Patients with intermediate Ki-67 expression (14% to 19%). (c) Patients with high Ki-67 expression (≥20%). (d) Number of patients and 10-year cumulative incidence. (e) Multivariable analysis. PgR, Progesterone receptor. Hazard ratios (HRs) and 95% confidence intervals (CIs) were calculated using a multivariable Cox proportional hazards regression model adjusted for pathologic tumor stage, pathologic node stage, tumor grade, peritumoral vascular invasion and menopausal status.