• Male or female aged 18 years or above;

• Can understand the purpose of clinical trials and the benefits and risks, voluntarily participate in and sign the informed consent

• The physical status score of the Eastern Oncology Consortium (ECOG) was ≤3;

• HER2-metastatic breast cancer confirmed histologically or cytologically (HER2- is defined as either a standard immunohistochemical (IHC) test result of 0 or 1+, or an IHC test result of 2+ and a negative ISH test result);

• Failure of standard treatment, or intolerance to standard treatment;

• pial metastasis is present, which is defined as meningeal metastasis confirmed by malignant tumor cells found in cerebrospinal fluid cytology; Or clinical symptoms/signs suggest meningeal metastasis, and brain MRI suggests pia enhancement;

• The function of major organs was good, which was confirmed by the following laboratory tests during the screening period:

• Platelet count ≥80\*10\^9/L

• Hemoglobin ≥8g/L

• Neutrophil count ≥1.5\*10\^9/L

• Serum creatinine ≤1.5\*ULN

• ALT and AST≤ 3\*ULN (if liver metastases are present, ALT and AST≤5\*ULN)

• Serum total bilirubin ≤1.5\*ULN

• International Standardized ratio (INR) and Activated partial thromboplastin time (APTT) ≤1.5\*ULN

• NYHA cardiac function grade ≤II, no obvious abnormality in ECG, or no clinical significance according to the investigators;

• Voluntary compliance with the trial protocol during the study period and regular follow-up;

⁃ For all women of childbearing age, fertile men or their spouses who did not plan to have children or donate sperm during the entire trial period until 6 months after the last dose, or who voluntarily took effective contraception, the blood/urine pregnancy test results of female patients of childbearing age within 7 days before enrollment were negative.

⁃ Subjects who have recovered from non-hematological toxicity from the last treatment (CTCAE≤ class 1, except for special conditions such as alopecia) before first administration, and who the investigator determines that the corresponding AE does not pose a safety risk.