Sacituzumab Govitecan and Intrathecal Chemotherapy for Treating Leptomeningeal Metastases From Her2-negative Breast Cancer

Inclusion Criteria: 1. A clear histopathologic diagnosis of breast cancer with HER2-negative subtype (including IHC 0, IHC 1+ or IHC 2+ and ISH negative); 2. Cerebrospinal fluid cytology confirms the presence of leptomeningeal metastases; or imaging findings combined with clinical symptoms and signs are consistent with the diagnosis of leptomeningeal metastases; 3. Age ≥ 18 years old. Exclusion Criteria: 1. Inadequate organ function: 1) Blood tests: ANC ≤ 1.5 x 10\^9/L, PLT ≤ 90 x 10\^9/L, Hb ≤ 90 g/L; 2) Blood biochemistry tests: TBIL ≥ 1.5 times the upper limit of normal; 3) ALT and AST ≥ 2.5 times the upper limit of normal; 2. Presence of serious and/or uncontrolled comorbidities that may affect participation: 1) Allergy to study drugs or adjuvant materials; 2) History of immunodeficiency (e.g., HIV-positive or other acquired or congenital immunodeficiency disease); 3) Severe concomitant diseases; 3. Pregnant and breastfeeding female patients; women of childbearing age who are unwilling or unable to use effective contraception; 4. Any other condition that, in the opinion of the investigator, makes the patient ineligible for participation in the study.