Inclusion Criteria:

          -  Provide informed consent

          -  Be able to communicate effectively with the study personnel

          -  Aged ≥18 years

          -  For Female Subjects

               -  Menopausal status

          -  Be postmenopausal as defined by the National Comprehensive Cancer Network as either:

               -  Age ≥55 years and one year or more of amenorrhea

               -  Age <55 years and one year or more of amenorrhea, with an estradiol assay <20
                  pg/mL

               -  Age <55 years and surgical menopause with bilateral oophorectomy

          -  Be premenopausal or perimenopausal on ovarian suppression with LHRH agonist for at
             least 4 months, with an estradiol assay <20 pg/mL and a negative urine pregnancy test.

          -  If subject is of child bearing potential, the subject must agree to use acceptable
             methods of contraception:

               -  If female study participant could become pregnant, use acceptable methods of
                  contraception from the time of the first administration of study medication until
                  6 months following administration of the last dose of study medication.
                  Acceptable methods of contraception are as follows: Condom with spermicidal
                  foam/gel/film/cream/suppository [i.e., barrier method of contraception], surgical
                  sterilization of male partner (vasectomy with documentation of azoospermia) and a
                  barrier method {condom used with spermicidal foam/gel/film/cream/suppository}

               -  If female study participant has undergone documented tubal ligation (female
                  sterilization), a barrier method (condom used with spermicidal
                  foam/gel/film/cream/suppository) should also be used

               -  If female study participant has undergone documented placement of an intrauterine
                  device (IUD) or intrauterine system (IUS), a barrier method (condom with
                  spermicidal foam/gel/film/cream/suppository) should also be used

          -  For Male Subjects

               -  Subject must agree to use acceptable methods of contraception:

          -  If the study subject's partner could become pregnant, use acceptable methods of
             contraception from the time of the first administration of study medication until 6
             months following administration of the last dose of study medication. Acceptable
             methods of contraception are as follows: Condom with spermicidal foam/gel/
             film/cream/suppository [i.e., barrier method of contraception], surgical sterilization
             (vasectomy with documentation of azoospermia) and a barrier method {condom used with
             spermicidal foam/gel/film/cream/suppository}, the female partner uses oral
             contraceptives (combination estrogen/progesterone pills), injectable progesterone or
             subdermal implants and a barrier method (condom used with spermicidal
             foam/gel/film/cream/suppository)

          -  If female partner of a study subject has undergone documented tubal ligation (female
             sterilization), a barrier method (condom used with spermicidal
             foam/gel/film/cream/suppository) should also be used

          -  If female partner of a study subject has undergone documented placement of an
             intrauterine device (IUD) or intrauterine system (IUS), a barrier method (condom with
             spermicidal foam/gel/film/cream/suppository) should also be used

          -  Eastern Cooperative Oncology Group (ECOG) performance status of ≤2

          -  Documented evidence of ER+/HER2- metastatic breast cancer

          -  Measurable disease is required as per RECIST 1.1 (NOTE: Bone only metastatic disease
             is acceptable but requires a measurable component

          -  Have androgen receptor nuclei staining ≥40% as assessed by central laboratory

          -  Received at least 2 prior lines of treatment in MBC setting which must have included
             both an AI (monotherapy or combination) and fulvestrant (monotherapy or combination);
             at least one must have been given in combination with a CDK 4/6 inhibitor.

          -  Previously responded (without disease progression for at least 6 months) to one of the
             following treatments: fulvestrant monotherapy or fulvestrant plus CDK 4/6 inhibitor or
             nonsteroidal aromatase inhibitor monotherapy or nonsteroidal aromatase inhibitor plus
             CDK 4/6 inhibitor for metastatic breast cancer.

          -  Subject is willing to comply with the requirements of the protocol through the end of
             the study

        Exclusion Criteria:

          -  Known hypersensitivity or allergy to enobosarm

          -  Alanine aminotransferase (ALT) or aspartate aminotransferase (AST) >2.5 X upper limit
             of normal (ULN) or total bilirubin >ULN (an elevated total bilirubin up to 1.5 X ULN
             attributed to a previously confirmed diagnosis of Gilbert's disease is acceptable if
             all other eligibility criteria are met). In patients with documented metastases to the
             liver, the limits for inclusion are ALT or AST >5.0 X ULN or total bilirubin >1.5 X
             ULN.

          -  Patients with biliary catheter.

          -  Creatinine clearance < 30 mL/min as measured using the Cockcoft Gault formula
             (patients with mild and moderate renal failure are not excluded from participation in
             this study)

          -  Previously received >1 course of systemic chemotherapy (not including immunotherapies
             or targeted therapies) for the treatment of metastatic breast cancer.

        Note: Subjects may have received 1 course of chemotherapy in the adjuvant or neoadjuvant
        setting would not count as a line of therapy.

          -  Subjects with radiographic evidence of central nervous system (CNS) metastases as
             assessed by CT or MRI that are not well-controlled (symptomatic or requiring control
             with continuous corticosteroid therapy [e.g., dexamethasone]) Note: Subjects with CNS
             metastases are permitted to participate in the study if the CNS metastases are
             medically well-controlled and stable for at least 30 days after receiving local
             therapy (irradiation, surgery, etc.)

          -  Radiotherapy within 14 days prior to randomization except in case of localized
             radiotherapy for analgesic purpose or for lytic lesions at risk of fracture, which can
             then be completed within 7 days prior to randomization. Subjects must have recovered
             from radiotherapy toxicities prior to randomization

          -  Any comorbid disease or condition (medical or surgical) which might compromise the
             hematologic, cardiovascular, endocrine, pulmonary, severe renal impairment,
             gastrointestinal, hepatic, or central nervous system; or other conditions that may
             interfere with the absorption, distribution, metabolism or excretion of study drug, or
             would place the subject at increased risk

          -  Treatment with any investigational product within < 4 half-lives for each individual
             investigational product OR within 30 days prior to randomization

          -  Major surgery within 30 days prior to randomization

          -  Treatment with testosterone, methyltestosterone, oxandrolone (Oxandrin®),
             oxymetholone, danazol, fluoxymesterone (Halotestin®), testosterone-like agents (such
             as dehydroepiandrosterone, androstenedione, and other androgenic compounds, including
             herbals), or antiandrogens (enzalutamide, abiraterone, bicalutamide, apalutamide, or
             darolutamide). Previous therapy with testosterone and testosterone-like agents is
             acceptable with a 30-day washout (if previous testosterone therapy was long term depot
             within the past 6 months, the site should contact the Medical Monitor) or any other
             androgenic agent.

          -  Treatment with any of the following hormone replacement therapies for metastatic
             breast cancer. Prior use in the adjuvant or neoadjuvant setting is allowed if the
             treatment is, discontinued greater than 30 days prior to randomization

               -  Estrogens

               -  Megesterol acetate

               -  Testosterone

          -  All other concurrent anticancer treatments (including, but not limited to, all SERMs
             unless randomized to the Control Treatment Group with a SERM as the control treatment,
             AIs unless randomized to Control Treatment Group (exemestane or exemestane plus
             everolimus) with the AI containing treatment as the control treatment, and all CDK 4/6
             inhibitors)

          -  An abnormal ECG result which, based on the investigator's clinical judgment, would
             place the subject at increased risk

          -  Has a known additional, invasive, malignancy that is progressing or required active
             treatment in the last 5 years [note: subjects with basal cell carcinoma of the skin,
             squamous cell carcinoma of the skin, ductal breast carcinoma in situ, bladder cancer
             (superficial treated), or cervical carcinoma in situ that have undergone potentially
             curative therapy are not excluded]

          -  Pregnant, lactating, or breastfeeding, or intending to become pregnant during the
             study or within 60 days after the final dose of study treatment