Real World Study of Pyrotinib in Human Epidermal Growth Factor Receptor-2 (HER2) Positive Breast Cancer

Inclusion Criteria: 1. ≥18 years old with histologically confirmed HER2 positive breast cancer. 2. Documented HER2 overexpression by local laboratory ,defined as immunohistochemistry (IHC) 3+ or fluorescence in situ hybridization (FISH) positive. 3. Physician has determined that treatment with pyrotinib is indicated. 4. Traceable medical record available. Exclusion Criteria: 1. Patients who are unable to understand the nature of the study and are unwilling to sign an informed consent . 2. Pregnant or breast feeding patients 3. Patients participating in any interventional clinical trial that includes investigational or marketed products at the time of enrollment. 4. Patients not suitable for this study under investigators' consideration.