There was no significant difference between the two groups in terms of age, ECOG status, BMI, tumor size, histologic grade, ki-67 expression, ER expression, PR expression, HER2 receptor expression, type of breast surgery, neoadjuvant chemotherapy regimen, clinical stage, pathological stage, Miller–Payne grade, hormonal therapy, radiation therapy, radiation time, platelet count at baseline, white blood cells at baseline, T-DM1 starting dose, complicated with thrombosis, previous ≥III-grade myelosuppression. Here, ESR1 is linked to neoplasm.