Inclusion Criteria:

          -  Pathologically confirmed diagnosis of breast cancer with radiographic evidence of
             incurable, unresectable, locally advanced or metastatic disease (LA/MBC)

          -  One of the following:

               -  Part A: Triple-negative disease (ER/PR/HER2-negative) and received at least 2
                  prior cytotoxic regimens in the incurable, unresectable, LA/MBC setting; or
                  ER-positive and/or PR-positive/HER2-negative disease and received at least 2
                  prior cytotoxic regimens in the incurable, unresectable, LA/MBC setting and are
                  no longer a candidate for hormonal therapy (not enrolling new patients);

               -  Part B: Combination Arm: HER2-positive disease and received at least 2 prior
                  cytotoxic regimens in the incurable, unresectable, LA/MBC setting (not enrolling
                  new patients);

               -  Part C: Triple-negative disease and received 2-4 prior non-hormonally-directed
                  therapies in the MBC setting (not enrolling new patients);

               -  Part D and Part E (dose-expansion cohort): Triple-negative disease and received 1
                  prior non-hormonally-directed or cytotoxic therapy in the MBC setting; or

               -  Part E: HR+(ER-positive and/or PR-positive)/HER2-negative disease who are
                  chemotherapy-eligible and not considered a candidate for further hormonal
                  therapy. Must have received no more than 1 prior non-hormonally-directed or
                  cytotoxic therapy in the LA/MBC setting.

          -  Part F: All of the following:

               -  Triple negative breast cancer

               -  No prior cytotoxic chemotherapy for unresectable locally advanced or metastatic
                  stage disease

               -  Tumor tissue PD-L1 expression CPS <10 expression

          -  Parts A, B, C, and D: Newly obtained or archived tumor tissue biopsy, must be
             collected for central pathology determination of LIV-1 expression

          -  Parts E and F: Archival or fresh baseline tumor sample is required.

          -  Measurable disease

          -  Eastern Cooperative Oncology Group performance status 0 or 1

          -  Combination Arm: adequate heart function

        Exclusion Criteria:

          -  Pre-existing neuropathy Grade 2 or higher

          -  Parts A, B, C, and D: Cerebral/meningeal disease that is related to the underlying
             malignancy and has not been definitively treated. Parts E and F: Known or suspected
             cerebral/meningeal metastasis that has not been definitively treated.

          -  Prior treatment with LV or prior treatment with an MMAE-containing therapy

          -  Combination Arm: hypersensitivity to trastuzumab