Neuro/Sacituzumab Govitecan/Breast Brain Metastasis/Glioblastoma/Ph 0

Inclusion Criteria: * At least 18 years of age * Histologically or cytologically documented breast cancer (Cohort A) with known or suspected parenchymal brain metastases. * Recurrent glioblastoma (Cohort B) with documented progression by RANO criteria following standard combined modality treatment with radiation and temozolomide. * Plans to undergo craniotomy as part of standard of care. Patients emergently needing surgical debulking due to symptoms of their disease are not eligible. * Recovered from toxicities of prior therapy to grade 0 or 1 * ECOG performance status ≤ 2. * Life expectancy of at least 3 months. * Acceptable liver function: * Bilirubin ≤ 1.5 times upper limit of normal * AST (SGOT) and ALT (SGPT) ≤ 3.0 times upper limit of normal (ULN); * Adequate renal function: calculated creatinine clearance ≥30mL/minute according to the Cockcroft and Gault formula * Acceptable hematologic status (without hematologic support) * ANC ≥1500 cells/uL * Platelet count ≥100,000/uL * Hemoglobin ≥9.0 g/dL * All women of childbearing potential must have a negative serum pregnancy test and male and female subjects must agree to use effective means of contraception (surgical sterilization or the use or barrier contraception with either a condom or diaphragm in conjunction with spermicidal gel or an IUD) with their partner from entry into the study through 6 months after the last dose. Exclusion Criteria: * The subject is receiving warfarin (or other coumarin derivatives) and is unable to switch to low molecular weight heparin (LMWH) before the first dose of study drug. * The subject has evidence of acute intracranial or intratumoral hemorrhage either by MRI or computerized tomography (CT) scan. Subjects with resolving hemorrhage changes, punctate hemorrhage, or hemosiderin are eligible. * The subject is unable to undergo MRI scan (eg, has pacemaker). * The subject has received enzyme-inducing anti-epileptic agents within 14 days of study drug (eg, carbamazepine, phenytoin, phenobarbital, primidone). * Patients whose only lesion undergoing resection has received stereotactic radiation within the past 3 months * The subject has received any of the following prior anticancer therapy: * Biologic agents (antibodies, immune modulators, vaccines, cytokines) within 21 days prior to first dose of study drug * Prior treatment with Sacituzumab Govitecan * Patients receiving UGT1A1 (Uridine diphosphate glucuronosyl transferase 1A1) inhibitors or inducers. * History of significant cardiovascular disease, defined as: * Congestive heart failure greater than New York Heart Association (NYHA) Class II according to the NYHA Functional Classification. * Unstable angina or myocardial infarction within 6 months before enrollment. * Serious cardiac arrhythmia. * Clinically significant ECG abnormality, including: * Marked Baseline prolonged QT/QTc interval (ie, a repeated demonstration of a QTc interval \>500 ms) demonstrated on ECG at Screening. * History of risk factors for torsade de pointes (eg, heart failure, hypokalemia, family history of long QT Syndrome). * Any medical or other condition which, in the opinion of the Investigator, causes the subject to be medically unfit to receive Sacituzumab Govitecan, or unsuitable for any other reason.