A Phase IIa Study to Evaluate NBQ72S

This is a single-arm, open-label study designed to evaluate the efficacy and safety of NBQ72S in patients with breast cancer leptomeningeal metastasis (with or without brain parenchymal metastasis). Patients will undergo screening prior to study entry. After screening successfully, they will receive intravenous infusion of NBQ72S. Treatment will continue until disease progression, unacceptable toxicity, withdrawal of informed consent, or any other conditions except as specified in the protocol (whichever occurs first). However, patients who demonstrate clinical benefits (despite radiological progression) with manageable toxicity, and are willing to continue receiving the NBQ72S, will be given the opportunity to continue treatment after the assessment and confirmation of Investigator. After treatment completion, patients will undergo safety follow-up and long-term survival follow-up until death or lost to follow-up.