Inclusion Criteria:

          1. Signed and dated written informed consent

          2. Subjects >= 18 years of age

          3. Eastern Cooperative Oncology Group (ECOG) performance status 0 or 1

          4. Clinical stage IV invasive breast cancer or unresectable locoregional recurrence of
             invasive breast cancer meeting the following criteria:

               -  Estrogen receptor (ER)/progesterone receptor (PR)-negative (=< 5% cells) by
                  immunohistochemistry (IHC) and human epidermal grow (HER2) negative (by IHC or
                  fluorescence in situ hybridization (FISH))

               -  Measurable disease as defined by Response Evaluation Criteria in Solid Tumors
                  (RECIST) version 1.1 criteria and which can be followed by computed tomography
                  (CT) or magnetic resonance imaging (MRI). A measurable lytic bone lesion(s)
                  and/or skin lesion(s) are allowed. Skin lesions must also be followed by
                  photography with measuring tools within the photograph at each tumor evaluation
                  time point. Ultrasound may be used to follow breast lesions not visible by CT
                  following discussion with Study Chair

               -  Amenable to biopsy at the time of study entry

               -  Known tumor/immune cell PD-L1 status by any assay

          5. Adequate organ function including:

               -  Cardiac ejection fraction at or above the institutional lower limit of normal, as
                  assessed by either echocardiogram or multigated acquisition (MUGA) scan

               -  Absolute neutrophil count (ANC) >= 1.0 x 10^9/L (may have received growth factor)

               -  Platelets >= 100 x 10^9/L

               -  Hemoglobin >= 9 g/dL (may have been transfused)

               -  Total serum bilirubin =< 1.5 times upper limit of normal (ULN)

               -  Aspartate aminotransferase (AST/serum glutamic oxaloacetic transaminase (SGOT))
                  and alanine aminotransferase (ALT/serum glutamate pyruvate transaminase (SGPT))
                  =< 2.5 x ULN (or =< 5 x ULN if liver metastases are present)

               -  Serum creatinine =< 1.5 x ULN or estimated creatinine clearance >= 50 mL/min as
                  calculated using the Cockcroft-Gault (CG) equation

               -  Prothrombin time (PT)/international normalized ratio (INR) =< 1.5 x ULN

               -  Thyroid stimulating hormone (TSH) within institutional normal limits (enrollment
                  of patients with TSH levels above or below the institutional normal limit in
                  situations where the patient has normal levels of triiodothyronine (T3) and free
                  thyroxine (FT4) may be allowed following discussion with study chair)

               -  Amylase =< 1 x ULN (Abnormality not of pancreatic origin is allowed)

               -  Lipase =< 1 x ULN (Abnormality not of pancreatic origin is allowed)

          6. Male and female patients of childbearing potential must agree to use at least two
             methods of acceptable contraception from 15 days prior to first trial treatment
             administration until at least 30 days after study participant's final dose of study
             drug(s)

             * NOTE: Females of childbearing potential are defined as those who are not surgically
             sterile or post-menopausal (i.e., patient has not had a bilateral tubal ligation, a
             bilateral oophorectomy, or a complete hysterectomy; or has not been amenorrhoeic for
             12 months without an alternative medical cause). Post-menopausal status in females
             under 55 years of age should be confirmed with a serum follicle-stimulating hormone
             (FSH) level within laboratory reference range for postmenopausal women

          7. Patients unable to read/write in English are eligible to participate in the overall
             study but will not participate in the Patient-Reported Outcome questionnaires
             throughout the trial.

          8. Re-enrollment of a subject that has discontinued the study as a pre-randomization
             screen failure (i.e., a consented patient who was not randomized and did not receive
             any study treatment) is permitted. If re-enrolled, the subject must be re-consented.
             Only the screening procedures performed outside of protocol-specified timing must be
             repeated; if biopsies and correlative blood samples were already obtained, and patient
             has not received any systemic anti-cancer therapy since they were obtained, they do
             not need to be repeated.

        Exclusion Criteria:

          1. More than 2 lines of chemotherapy in the metastatic setting

          2. More than 1 prior line of checkpoint inhibitor therapy in the metastatic setting

          3. Prior treatment with sacituzumab, govitecan

          4. Concurrent anticancer therapy. Required washout from prior therapies are as follows:

               -  Chemotherapy: >= 14 days

               -  Major surgery: >=14 days (provided wound healing is adequate)

               -  Radiation: >= 7 days

               -  Investigational/biologic therapy (half-life =< 40 hours): >= 14 days

               -  Investigational/biologic therapy (half-life > 40 hours): >= 28 days

               -  Use of corticosteroids or immunosuppressive medication is exclusionary, except
                  the following in the absence of active autoimmune disease:

                    -  Subjects are permitted the use of corticosteroids with minimal systemic
                       absorption (e.g. topical, ocular, intra-articular, intranasal, and inhaled)

                    -  Systemic corticosteroids at physiologic doses =< 10 mg/day of prednisone or
                       equivalent are permitted

                    -  Adrenal replacement steroid doses including doses > 10 mg daily prednisone
                       are permitted

                    -  A brief (less than 3 weeks) course of corticosteroids for prophylaxis (e.g.
                       CT scan premedication against contrast dye allergy) or for treatment of
                       nonautoimmune conditions (e.g. delayed-type hypersensitivity reaction caused
                       by a contact allergen) is permitted

          5. Previous malignant disease other than breast cancer within the last 5 years, with the
             exception of basal or squamous cell carcinoma of the skin, cervical carcinoma in situ,
             or low-risk cancers considered curatively treated (i.e. complete remission achieved at
             least 2 years prior to first dose of study drugs AND additional therapy not required
             while receiving study treatment)

          6. All subjects with central nervous system metastases and/or carcinomatous meningitis,
             except those meeting the following criteria::

               -  Brain metastases that have been treated locally and are clinically stable for at
                  least 2 weeks prior to enrollment

               -  No ongoing neurological symptoms that are related to the brain localization of
                  the disease (sequelae that are a consequence of the treatment of the brain
                  metastases are acceptable)

               -  Subjects must be either off steroids or on a stable or decreasing dose of =< 10
                  mg daily prednisone (or equivalent)

          7. Receipt of any organ transplantation including allogeneic stem-cell transplantation

          8. Significant acute or chronic infections including, among others:

               -  Known history of testing positive for human immunodeficiency virus (HIV), or
                  acquired immunodeficiency syndrome (AIDS); testing is not required for this
                  protocol.

               -  A history of a positive test for hepatitis B virus (HBV) surface antigen (and/or
                  core antibody) and/or confirmatory hepatitis C virus (HCV) ribonucleic acid (RNA)
                  (if anti-HCV antibody tested positive); testing is not required for this protocol

          9. Active autoimmune disease with reasonable possibility of clinically significant
             deterioration when receiving an immunostimulatory agent:

               -  Subjects with type 1 diabetes mellitus, vitiligo, psoriasis, hypo- or
                  hyperthyroid disease not requiring immunosuppressive treatment are eligible

               -  Subjects requiring hormone replacement with corticosteroids are eligible if the
                  steroids are administered only for the purpose of hormonal replacement and at
                  doses =< 10 mg or 10 mg equivalent prednisone per day

               -  Administration of steroids through a route known to result in a minimal systemic
                  exposure (topical, intranasal, intro-ocular, or inhalation) is acceptable

         10. History of interstitial lung disease that is symptomatic or which may interfere with
             the detection or management of suspected drug-related pulmonary toxicity

         11. Uncontrolled asthma (defined as having 3 or more of the following features of
             partially controlled asthma within 28 days prior to starting study treatment: Daytime
             symptoms more than twice per week, any limitation of activities, any nocturnal
             symptoms/awaking, need for reliever/rescue inhaler more than twice per week, or known
             lung function [peak expiratory flow (PEF) or forced expiratory volume in 1 second
             (FEV1)] without administration of a bronchodilator that is < 80% predicted or personal
             best [if known])

         12. Current symptomatic congestive heart failure (New York Heart Association > class II),
             unstable cardiac arrhythmia requiring therapy (e.g. medication or pacemaker), unstable
             angina (e.g. new, worsening or persistent chest discomfort), uncontrolled hypertension
             (systolic > 160 mmHg or diastolic > 100mmHg), or known cardiac ejection fraction below
             the lower limit of institutional normal. Or any of the following occurring within 6
             months (180 days) prior to first dose of avelumab: Myocardial infarction,
             coronary/peripheral artery bypass graft, cerebrovascular accident or transient
             ischemic attack. (Use of antihypertensive medication to control blood pressure is
             allowed.)

         13. Patients who have neuromuscular disorders that are associated with elevated creatine
             kinase (CK)

         14. History of acute or chronic pancreatitis

         15. History or current evidence of retinal vein occlusion (RVO), or current risk factors
             for RVO including uncontrolled glaucoma, ocular hypertension, history of
             hyperviscosity, or hypercoagulability syndromes (patients with a history of pulmonary
             embolism or deep vein thrombosis (DVT) are allowed on study if they are also on
             anticoagulation as noted in (16) below) ; history of retinal degenerative disease.

         16. Requirement of anticoagulant therapy with oral vitamin K antagonists such as Coumadin
             (warfarin). Low-dose anticoagulants for the maintenance of patency in a central venous
             access device or the prevention of deep vein thrombosis or pulmonary embolism is
             allowed. Therapeutic use of low molecular weight heparin or factor Xa inhibitors are
             allowed provided patients are safely able to interrupt it prior to biopsy procedures.

         17. Persisting toxicity related to prior therapy that has not reduced to grade 1 (National
             Cancer Institute Common Toxicity Criteria for Adverse Events (NCI CTCAE) version 5.0);
             however, alopecia and sensory neuropathy grade =< 2 is acceptable

         18. Known severe (grade >= 3 NCI-CTCAE v5.0) hypersensitivity reactions to monoclonal
             antibodies, or history of anaphylaxis

         19. Vaccination within 28 days of the first dose of study drugs and while on trial is
             prohibited, except for administration of inactivated vaccines (for example,
             inactivated influenza vaccine)

         20. Pregnant or breastfeeding females

         21. Known current alcohol or drug abuse

         22. Prisoners or subjects who are involuntarily incarcerated

         23. Known psychiatric condition, social circumstance, or other medical condition
             reasonably judged by the patient's study physician to unacceptably increase the risk
             of study participation; or to prohibit the understanding or rendering of informed
             consent or anticipated compliance with scheduled visits, treatment schedule,
             laboratory tests and other study requirements.