A Two-cohort Study of SHR-A1811 in the Treatment of HER2-positive Breast Cancer With Brain Metastases

Systemic therapy: 4.8 mg/kg administered as an intravenous infusion on Day 1 of each cycle. 3 weeks a cycle. Continuous medication until study completion, occurrence of intolerable toxicity, disease progression, withdrawal from the study for any reason, or death, whichever occurs first, or until the investigator deems that the patient would no longer benefit from the treatment.

Intrathecal therapy: Administered intrathecally on Day 1 of each cycle. Dose escalation follows a Bayesian Optimal Interval (BOIN) design with three predefined dose levels-15 mg, 30 mg, and 40 mg. The starting dose level is 15 mg. Patients are enrolled in cohorts of three per dose level. If no dose-limiting toxicities (DLTs) are observed, escalation proceeds to the next higher dose level according to the BOIN algorithm. Treatment is administered for a minimum of two cycles and is continued until cerebrospinal fluid (CSF) cytology achieves negative conversion, completion of six cycles, or intolerable adverse events, whichever occurs first. Extension beyond six cycles may be permitted following investigator's discussion and must be documented with justification.

radiotherapy is determined by investigator's choice