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.