Primary Objective~1. Test of the preliminary efficacy of the intracranial anti tumor activity of QBS72S through overall response rate (ORR) in Cohort 1 (Stages 1+2).~Secondary Objectives~Test of the preliminary efficacy of the intracranial anti tumor activity of QBS72S through progression free survival (PFS) in Cohort 1 (Stages 1+2).~Test of the preliminary efficacy of the intracranial anti tumor activity of QBS72S through overall survival (OS) in Cohort 1 (Stages 1+2).~Test of the preliminary efficacy of the intracranial anti tumor activity of QBS72S through durations of response (DoR) in Cohort 1 (Stages 1+2).~Evaluate safety of QBS72S treatment in Cohort 1 (Stages 1+2), and Cohort 2.
This study is to evaluate the efficacy and safety of QBS72S in participants with advanced, relapsed, metastatic breast cancer with CNS involvement.