The primary objective of the study is to study the pharmacokinetics of pyrotinib and docetaxel plus Trastuzumab in HER2 Positive MBC.

The secondary objective of the study is to evaluate the safety and efficacy (ORR) of pyrotinib and docetaxel plus Trastuzumab in HER2 Positive MBC.

Inclusion Criteria:

1. HER2 positive recurrent or metastasis breast cancer.
2. Eastern Cooperative Oncology Group (ECOG) performance status 0 or 1.
3. Adequate organ function.
4. Signed, written inform consent obtained prior to any study procedure.

Exclusion Criteria:

1. Patients received more than 1 line of chemotherapy or immunotherapy in the phase of recurrence / metastasis.
2. History of HER tyrosine kinase inhibitors or monoclonal antibody for breast cancer in any treatment setting，except trastuzumab ,or Pertuzumab used in the neo-adjuvant or adjuvant setting.
3. Assessed by the investigator to be unable receive systemic chemotherapy.
4. History of other malignancy within the last 5 years，except for carcinoma in situ of cervix，basal cell carcinoma or squamous cell carcinoma of the skin that has been previously treated with curative intent.
5. Pregnant or lactating women，or for women of childbearing potential unwilling to use a highly-effective contraception during of the study treatment and for at least 7 months after the last dose of study treatment.