Predictive Value of Magee Equation 3 for Tumor and Axillary Response to Neoadjuvant Chemotherapy in HR-Positive, HER2-Negative Breast Cancer

Background Hormone receptor-positive (HR+), HER2-negative breast cancer demonstrates limited chemosensitivity, making patient selection for neoadjuvant chemotherapy (NACT) a challenge. The Magee Equation 3 (ME3), derived from routine immunohistochemistry, provides a cost-effective surrogate for genomic assays. This study aimed to evaluate the predictive value of ME3 for both primary tumor and axillary response to NACT in HR+/HER2– breast cancer. Methods We retrospectively analyzed 116 patients with HR+/HER2– breast cancer who received NACT between 2018 and 2023. Magee Equation 3 scores, calculated from ER, PR, HER2, and Ki-67 data, were stratified into low (31) categories. Pathological complete response (pCR) and axillary response were assessed using Residual Cancer Burden criteria. Receiver operating characteristic (ROC) analyses determined optimal ME3 cut-offs. Results Overall, 16.4% of patients achieved tumor pCR, and 59.5% achieved axillary response. No patients with ME3 31.2 as the optimal cut-off for tumor pCR (AUC 0.863, sensitivity 78.9%, and specificity 87.6) and >22.5 for axillary response (AUC 0.887, sensitivity 78.3%, and specificity 85.1). Discussion Magee Equation 3 is a strong predictor of both tumor and axillary response following NACT in HR+/HER2– breast cancer. By offering a practical and inexpensive alternative to genomic assays, ME3 may support treatment decision-making, particularly for axillary management, and has the potential to expand clinical utility in settings where genomic testing is limited.