Pathological complete response (pCR) after NAC is a strong predictor of favorable outcomes, especially in aggressive breast cancer subtypes such as human epidermal growth factor receptor 2-positive (HER2+) breast cancer and triple-negative breast cancer (TNBC; lacking estrogen receptor (ER), progesterone receptor (PR), and HER2 overexpression) [3,4]. This evidence concerns the gene ESR1 and breast cancer.