The aim of this project is to evaluate whether the sequence of Trastuzumab，pyrotinib and Nab-Paclitaxel in first line followed by SHR-A1811 in second line is superior to the sequence of SHR-A1811 in first line followed by Trastuzumab，pyrotinib and Nab-Paclitaxel in second line for HER2 positive breast cancer brain metastases.

Inclusion Criteria:

1. Females ≥18 yrs old
2. Pathologically confirmed HER2-positive advanced breast cancer;
3. Newly diagnosed brain metastes,At least one measurable intracranial lesion
4. Not received any systemic treatment for advanced stage
5. Radiotherapy was allowed in patients with an urgent need for control of intracranial symptoms
6. Adequate function of major organs
7. Willing to join in this study, able to provide written informed consent, good compliance and willing to cooperate with follow-up.

Exclusion Criteria:

1.Has leptomeningeal metastasis or cystic metastatic lesions confirmed by MRI or lumbar puncture; 2.Existence of third space fluid (e.g. massive ascites, pleural effusion, pericardial effusion) that is not well controlled by effective methods, e.g. drainage; 3.Has received whole brain radiotherapy, chemotherapy, surgery within 2 weeks before first dose of study therapy; 4.Has known clinically significant lung disease, that is, moderate-to-severe lung disease which severely affects respiratory function, including but not limited to: idiopathic pulmonary fibrosis, pneumonitis. Prior ≥ grade 3 interstitial lung disease is not allowed to enrolment; 5.Has received full-dose anticoagulants or thrombolytics within 10 days before enrolment, or non-steroid anti-inflammatory drugs with platelet inhibition 6.Previous treatment with trastuzumab deruxtecan (DS-8201a) or any other antibody drug conjugate (ADC) which consists of an exatecan derivative that is a topoisomerase 1 inhibitor; 7.Participated in other drug clinical trials within 4 weeks before admission; 8.Other malignant tumors, excluding cured cervical carcinoma in situ, skin basal cell carcinoma or skin squamous cell carcinoma, have been diagnosed in the past five years.

-