Overtreatment in Hormone Receptor Positive, HER2-, Axillary Node Negative, Non-Metastatic Early Breast Cancer

Abstract

HR+ HER2- T1 N0 M0 breast cancer has very low 5-year postoperative risk of relapse (<5%) with current SoC treat- ment regimens: endocrine monotherapy or chemoendocrine com- bination therapy. Minimally aggressive treatment is ideal. Absent gene-profiling, histopathological features of the tumor are exam- ined to predict risk of relapse. This paper establishes statistical evidence for use of an empirical prognostic index as a risk-based clinical decision aid where gene profiles are unavailable. Methods: A retrospective cohort (n=965) observed for 5 years was propensity score (PS) matched to correct baseline risk differences between chemoendocrine therapy and endocrine monotherapy treatment groups. PS were generated from logistic regression of pertinent histopathological covariates available to a clinician at the time of diagnosis onto treatment designation. Comparator groups were fur- ther equilibrated using Synthetic Minority Over-Sampling (SMOTE). Estimated treatment effects were assessed after propensity score- matching (PSM) and after SMOTE-normalized re-sampling. Results: Propensity score-matched groups (n=262) showed no difference in relapse rates between groups. Significant differences in histopatho- logical covariates remained between groups after PSM. SMOTE further minimized inter-group differences.