An Extended Cox Prognostic Model of ER/PR+ and HER2− Breast Cancer Patients

Abstract

Background: The purpose of this study was to explore a new ER/PR+ and HER2− breast cancer prognostic model called the extended Cox prognostic model by us for determining the cut-off values for multiple continuous prognostic factors and their interaction via the new modeling idea and variable selection method. Methods: A total of 335 patients with ER/PR+, HER2- breast cancer were enrolled for the final analysis. The primary endpoint was breast cancer-specific mortality (BCSM). The prognostic factors (histological grade, histological type, stage, T, N, lymphovascular invasion, P53, Ki67, ER, PR, age) were included in this study. The four continuous valuables (Ki67, ER, PR, age) were partitioned into a series of binary variables which all were fitted in the multivariate Cox analysis. A smoothly clipped absolute deviation (SCAD) variable selection method was used. Model performance was expressed in discrimination and calibration. Results: We developed an extended Cox model with a time threshold at 164 weeks (more than 3 years) post-operation. We found that the cut-off values for PR, Ki67 and age were 20%, 60% and 41-55 years respectively. There was interaction between age and PR for the patients with age≥41years and PR≥20% after 164 weeks post-operation. The patients with age≥41years and PR≥20% after 164 weeks post-operation had relatively higher mortality than before 164 weeks postoperatively. Conclusions: Our study would offer the guidance in the prognosis for the patients with ER/PR+ and HER2− breast cancer in China. The new idea would be one of ideas for modeling and determining the cut-off values of prognostic factors in future.