Percentage of Hormone Receptor Positivity in Breast Cancer Provides Prognostic Value: A Single-Institute Study

BACKGROUND: A majority of breast cancer tumors express estrogen receptor (ER) and/or progesterone receptor (PR); however, the percentage of cancer cells expressing these receptors can range from 0-100%. The prognostic and therapeutic impact of the percentage of cells expressing hormone receptors in breast cancer is not fully understood. METHODS: A retrospective analysis of 411 breast cancer patients who were treated at the University of Nebraska Medical Center between 2010 and 2017 was performed. Patient tumors were evaluated for percentage of cells expressing ER and PR in conjunction with clinical outcomes. RESULTS: Patient tumors demonstrated a highly bimodal pattern of ER and PR staining with a majority of tumors demonstrating either a high percentage (> 80% of cells) or lack of cells (0%) staining for ER or PR. An increase in the percentage of ER positivity correlated with decreased local recurrence and improved overall survival. An increase in the percentage of PR positivity demonstrated a trend towards decreased local recurrence and improved overall survival, but was not statistically significant. CONCLUSIONS: Results based on both continuous and categorical evaluation of ER expression revealed that increasing expression correlated with improved patient outcomes. Similar evaluation of PR expression demonstrated a trend towards improved patient outcomes though not statistically significant. These findings suggest that the degree of hormone receptor positivity and not a Boolean representation of positivity could provide additional prognostic value in the treatment and management of breast cancer.