Inclusion Criteria:

          -  Life expectancy of > 6 months, as determined by the investigator

          -  Ability to understand and the willingness to sign a written informed consent document

          -  Histologically or cytologically confirmed metastatic breast carcinoma

          -  Stage IV or recurrent disease with distant metastases

          -  Participants must have experienced disease progression after at least two lines of
             standard treatment modalities and/or one prior line of cytotoxic chemotherapy (not
             just endocrine therapy)

          -  Participants must have at least one measurable site of disease as defined by Response
             Evaluation Criteria in Solid Tumors (RECIST) version (v1).1 that is amendable to
             biopsy

          -  Confirmed presence of SSTR based on gallium Ga 68-HA-DOTA-TATE (68Ga DOTATATE) uptake
             with Krenning score >= 2 on positron emission tomography [PET] imaging of target
             lesions (per radiologist's assessment)

          -  Participants must have fully recovered from the acute toxic effects of all prior
             treatment to grade 1 or less, except alopecia and =< grade 2 neuropathy which are
             allowed

          -  Participant must have Eastern Cooperative Oncology Group (ECOG) performance status =<
             2

          -  Participant must consent to undergo a pre-treatment screening biopsy for enrollment

          -  Hemoglobin >= 8.0 g/dL with no blood transfusion in the past 28 days (measured within
             28 days prior to administration of study treatment)

          -  Absolute neutrophil count (ANC) >= 2.0 x 10^9/L (measured within 28 days prior to
             administration of study treatment)

          -  Platelet count >= 75 x 10^9/L (measured within 28 days prior to administration of
             study treatment)

          -  Total bilirubin =< 3 x institutional upper limit of normal (ULN) (measured within 28
             days prior to administration of study treatment)

          -  Aspartate aminotransferase (AST)/alanine aminotransferase (ALT) =< 2.5 x institutional
             upper limit of normal (unless liver metastases are present in which case they must be
             =< 5 x ULN) (measured within 28 days prior to administration of study treatment)

          -  Serum albumin >= 3.0 g/L, unless prothrombin time or international normalized ratio
             (INR) value is within the normal range (measured within 28 days prior to
             administration of study treatment)

          -  Participants must have serum creatinine =< 1.7 mg/dL, or creatinine clearance
             estimated of >= 51 mL/min using the Cockcroft-Gault equation or based on a 24 hour
             urine test (measured within 28 days prior to administration of study treatment)

          -  Female participants of childbearing potential (FOCBP) must have a negative urine or
             serum pregnancy test within 72 hours prior to receiving the first dose of study
             medication. If the urine test is positive or cannot be confirmed as negative, a serum
             pregnancy test will be required

          -  FOCBP agree to use a highly-effective method of contraception starting with the first
             dose of study therapy through 6 months after the last dose of study therapy

               -  FOCBP are those who are not proven postmenopausal. Postmenopausal is defined as:

                    -  Amenorrheic for > 24 consecutive months following cessation of exogenous
                       hormonal treatments

                    -  Luteinizing hormone (LH) and Follicle stimulating hormone (FSH) levels in
                       the post menopausal range for women under 50 years of age

                    -  Radiation-induced oophorectomy with last menses > 1 year ago

                    -  Chemotherapy-induced menopause with > 1 year interval since last menses

                    -  Surgical sterilization (bilateral oophorectomy or hysterectomy or tubal
                       ligation)

        Exclusion Criteria:

          -  Currently participating and receiving study therapy or has participated in a study of
             an investigational agent and received study therapy or used an investigational device
             within 4 weeks of first dose of 177Lu- DOTATATE treatment

               -  Individuals in the follow-up phase of a prior investigational study may
                  participate as long as it has been 4 weeks since last dose of the previous
                  investigational agent or device

          -  Prior external beam radiation therapy to more than 25% of the bone marrow

          -  Other malignancy unless curatively treated with no evidence of disease for >= 5 years
             except: adequately treated non-melanoma skin cancer or curatively treated in situ
             cancer of the cervix

          -  Known brain metastases, unless these metastases have been treated and stabilized

          -  Peptide receptor radionuclide therapy at any time prior to study enrollment

          -  Known hypersensitivity to somatostatin analogues or any component of the 68Ga-
             DOTATATE or 177Lu- DOTATATE formulations

          -  Patients with uncontrolled infection will not be enrolled until infection is treated
             per provider discretion

          -  Uncontrolled intercurrent illness including, but not limited to, symptomatic
             congestive heart failure, unstable angina pectoris, serious cardiac arrhythmia,
             myocardial infarction within 6 months prior to enrollment, New York Heart Association
             (NYHA) class III or IV heart failure

          -  Uncontrolled diabetes mellitus as defined by a fasting blood glucose

          -  Any patient receiving treatment with short-acting somatostatin analogs, which cannot
             be interrupted for both 24 hours before and after the administration of 177Lu, or any
             patient receiving treatment with long-acting release somatostatin analogs that cannot
             be interrupted for at least 4 weeks before the administration of 177Lu- DOTATATE

          -  Any surgery or radiofrequency ablation within 12 weeks prior to enrollment in the
             study; or prior radioembolization; chemoembolization; or external beam radiation
             therapy (EBRT) to > 25% of bone marrow, at any time

          -  Any chemotherapy or targeted therapy within 4 weeks prior to enrollment in the study

          -  Current spontaneous urinary incontinence making impossible the safe administration of
             the radioactive study agent

          -  Any psychiatric illness that prevents patient from informed consent process

          -  Any concurrent condition that, in the Investigator's opinion, would jeopardize the
             safety of the patient or compliance with the protocol

          -  Participant is pregnant or breastfeeding, or expecting to conceive within the
             projected duration of the trial, starting with the screening visit through 6 months
             after the last dose of trial treatment