ERBB2 and breast cancer: The proportion of HER2-low in triple negative breast cancer (TNBC) patients is significant, and the effect of changes in HER2 expression before and after NAC on the prognosis of TNBC is not yet known; therefore, the aim of this study was to evaluate the differences in clinicopathological characteristics, efficacy of NAC and prognosis in patients with HER2-zero and HER2-low HR-negative BC, as well as the effect of HER2-evolution on the prognosis of HER2 before and after NAC.