When Ki-67 expression was categorized according to the corresponding median values in each biological subgroup, we found that patients with high pre-NACT Ki-67 had higher pCR rates in ER+/HER2− BC (n = 1091, 13.1% vs. 4.4% in Ki-67 high vs. low, respectively; p < 0.0001), TNBC (n = 543, 40.1% vs. 29.2% in Ki-67 high vs. low, respectively; p = 0.0107) and HER2+ BC (n = 820, 51.7% vs. 39.7% in Ki-67 high vs. low, respectively; p = 0.0008). The gene discussed is ESR1; the disease is breast cancer.