The different rates in achieving a pCR can be partially explained by the heterogeneity of breast cancer, as the patient's tumor stage, histologic grade, age, hormonal status (estrogen receptor [ER], progesterone receptor [PR]), and human epidermal growth factor receptor 2 (HER2) status, as clinicopathological characteristics are closely associated with the probability of achieving a pCR.8 This evidence concerns the gene ESR1 and breast cancer.