RESUMEN
Aim: The aim of the study was to assess the role of Magee Equation 3 (MagEq3), IHC4 score, and HER2-low status in predicting "satisfactory response (SR)" to neoadjuvant chemotherapy (NAC) in HR+/HER2- breast cancer (BC) patients. Methods: In a retrospective study, female patients of any age with T1-4, N0-2, M0 HR+/HER2- BC who received NAC and underwent adequate locoregional surgical treatment were included. Patients were grouped according to 2 outcomes: (a) overall response to NAC in breast and axilla by using residual cancer burden (RCB) criteria and (b) axillary downstaging after NAC by using N staging. 2 cohorts for overall response were overall SR (RCB 0-1) and no SR (RCB 2-3). On the other hand, for axillary downstaging, 2 cohorts constituted from axillary SR (ypN0 and ypN0i+) and no SR (ypNmic-N3). MagEq3 and IHC4 scores were calculated from their pathological tumor slides in each patient. HER2 status was categorized as either "no" or "low." In addition, patient age, family history, tumor histology, stage at admission, and Ki-67 status were compared between cohorts according to predefined outcomes. Results: In a total of 230 BC patients, 228 patients were included to compare according to their RCB levels. The mean age of patients with overall SR was significantly lower than those without. Patients with high Ki-67 expression, high (>30) MagEq3 score, high ICH4 quartile, and HER2-low status had significantly more overall SR. On the other hand, only patients with high Ki-67 expression had significantly more axillary SR. MagEq3 score levels, ICH4 quartiles, and HER2 status were similar between patients with axillary SR and not. Conclusion: MagEq3 and IHC4 tools seemed to be useful to predict those HR+/HER2- BC patients who are most likely to get benefit from NAC. But, only high Ki-67 expression level significantly predicted satisfactory axillary downstaging in HR+/HER2- BC patients.