Pre-Treatment Ki67 Index for Everolimus Efficacy in Patients with Hormone Receptor-Positive and Human Epidermal Growth Factor Receptor 2-Negative Advanced Breast Cancer: A Multicenter Cohort Study

Purpose: The study aims to explore the predictive value of the Ki67 index for everolimus efficacy in patients with hormone receptor-positive and human epidermal growth factor receptor 2-negative (HR+/HER2-) advanced breast cancer (ABC). Materials and Methods: We collected data on 2,518 cancer patients who received everolimus treatment from three cancer centers in China. Their clinicopathologic characteristics were retrospectively collected. A training cohort and a validation cohort were developed. Results: A total of 300 patients with HR+/HER2- ABC were included in the study, with 200 patients in the training cohort and 100 patients in the validation cohort. When analyzing the Ki67 index from 14% to 50%, only the Ki67 cut-off of 40% was found to be significantly correlated with progression-free survival (PFS) for patients in the training cohort. Multivariate Cox analyses further showed that Ki67 index of 40% (p=0.03) was significantly associated with PFS in patients treated with everolimus. Patients with Ki67 less than 40% had an improved PFS of 7.0 months, significantly better than 4.6 months for patients with Ki67 more than 40% (p=0.03, HR=0.67, 95CI%=0.46-0.97). In the validation cohort, patients with a Ki67 index of less than 40% had a significantly longer PFS of 4.3 months (2.1 months versus 4.3 months, p