A Phase IIa Study to Evaluate NBQ72S

Inclusion Criteria: * The patient must have histological evidence confirming the diagnosis of breast cancer with leptomeningeal metastasis: a. Breast cancer must be diagnosed through biopsy from either the primary or metastatic sites; b. Leptomeningeal metastasis (with or without brain parenchymal metastases) must be confirmed by imaging examinations(MRI), or by positive or suspicious cerebrospinal fluid cytology; c. There is no restriction on the duration of prior systemic therapy for the primary tumor. * The patient's Karnofsky Performance Status (KPS) must be ≥60. * The patient must have adequate bone marrow function, including: 1. Absolute neutrophil count (ANC) ≥1,500/mm³ or ≥1.5 x 10⁹/L; 2. Platelet count ≥100,000/mm³ or ≥100 x 10⁹/L; 3. Hemoglobin ≥9 g/dL; * The patient must have adequate renal function, including: a. Serum creatinine ≤1.5 x upper limit of normal (ULN) or estimated creatinine clearance ≥50 mL/min. Note: In equivocal cases, a 24-hour urine collection test can be used to estimate the creatinine clearance more accurately; * The patient must have adequate hepatic function, including: 1. Total serum bilirubin ≤1.5 x ULN; if the tumor involves the liver, or if the patient has a history of Gilbert's syndrome, total bilirubin must be \<3 x ULN; 2. Aspartate aminotransferase (AST) and alanine aminotransferase (ALT) ≤2.5 x ULN; if the tumor involves the liver, these values must be ≤5.0 x ULN; * Females of childbearing potential and males with fertile partners must agree to use effective contraception during the study and for 7 months following the last dose of study treatment; Exclusion Criteria: * Patients with any other active malignancies unrelated to the primary tumor, except for those with basal cell carcinoma, squamous cell carcinoma, or in situ carcinoma that have been adequately treated. * Patients who are intolerant to any substance in the investigational product, including sulfobutylether-β-cyclodextrin, mefenamic acid, bendamustine, chloramphenicol, or any nitrogen mustard chemotherapy agents, or who have experienced a severe (Grade ≥3) allergic or hypersensitivity reaction to these substances. * Patients who have received a live vaccine or experimental drug within 30 days prior to Cycle 1, Day 1 (C1D1). * Pregnant or breastfeeding patients. * Any other conditions that may affect the patient's eligibility for this study in the judgment of the investigator