Inclusion Criteria:  Diagnosis of breast cancer based on International statistical classification of diseases and related health problems 10th revision (International Statistical Classification of Diseases and Related Health Problems [ICD-10]) (C50.xx) Received at least one prescription of endocrine therapy drugs Diagnosis of secondary malignant neoplasm based on ICD-10 (C77.x, C78.x, C79.x )  Exclusion Criteria:  -Received a prescription of anti-HER2 therapy (Trastuzumab, Trastuzumab emtansine, Pertuzumab, and Lapatinib tosilate hydrate)