This study aims to evaluate the safety, tolerability, PK and preliminary anti-tumour activity of SHR-A1811 combined with other therapies in patients with HER2 low advanced or metastatic breast cancer.

Inclusion Criteria:

1. Ability to give informed consent, signed and dated IRB/EC approved informed consent, willing and able to comply with treatment planning visits, tests and other procedural requirements
2. When signing the informed consent, the age is 18-75 years old (including both ends), female patients who have pathologically documented HER2 low breast cancer
3. ECOG Performance Status of 0 or 1
4. Patient must have adequate tumor sample for biomarker assessment
5. At least one measurable lesion
6. Adequate organ function

Exclusion Criteria:

1. There are untreated or active central nervous system (CNS) tumor metastases
2. There was a third space effusion that could not be controlled by drainage (such as a large number of ascites, pleural effusion and pericardial effusion)
3. Major surgery within 4 weeks prior to enrollment
4. Has multiple primary malignancies within 5 years, excluding cured basal cell carcinoma of skin, cervical carcinoma in situ, papillary thyroid carcinoma, etc
5. Has current ILD/pneumonitis, or where suspected ILD/pneumonitis cannot be ruled out at screening
6. Uncontrolled intercurrent illness
7. Uncontrolled or significant cardiovascular disease
8. Has known human immunodeficiency virus (HIV) infection, or active hepatitis B or C infection.
9. According to NCI-CTCAE v5.0 classification, those who have not recovered to grade Ⅰ toxicity caused by previous anti-tumour treatment