Exploring the differences in chemotherapy sensitivity and prognosis between HER2-low BC and HER2-zero BC can help us further discover the differences between HER2-low BC and HER2-zero BC, and also help us better understand the clinicopathological characteristics of HER2-low BC and its sensitivity to chemotherapy, to provide a basis for the later formulation of HER2-low BC treatment plan. The gene discussed is ERBB2; the disease is breast cancer.