Inclusion Criteria:

          1. Histologically confirmed, unresectable, locally advanced or metastatic solid cancers:

               -  Part 1 (Dose-Escalation): All HER2-positive solid cancers are eligible

               -  Part 2 (Dose-Expansion): Any type of HER2-positive solid cancer, including breast
                  cancer, gastric or gastroesophageal adenocarcinomas (GEA).

          2. HER2-positive in the latest tumor sample tested for HER2 (testing to be done on a
             metastatic lesion in cases of metastatic cancers).

          3. Relapsed or refractory to or intolerant of existing therapy(ies)

          4. At least 1 measurable or evaluable lesion according to RECIST 1.1

          5. ECOG performance score of ≤ 1

          6. Bone marrow function:

               -  Absolute neutrophil count (ANC) ≥ 1,000/mm3

               -  Platelet count ≥ 75,000 mm³ and

               -  Hemoglobin ≥ 8.0 g/dL

               -  No red blood cell transfusion within 4 weeks of study treatment start is allowed

          7. Kidney function:

               -  (eGFR) ≥ 50 mL/min calculated by the Cockcroft-Gault formula

               -  Subjects with CLcr ≥ 50 mL/min will be eligible irrespective of the eGFR result

          8. Cardiac Function:

               -  Left ventricular ejection fraction (LVEF) ≥ 55% on the multigated acquisition
                  (MUGA) scan (preferred) or echocardiogram (ECHO) assessment, and

               -  QTcF ≤ 480 ms for women and QTcF ≤ 450 ms for men [average from three QTcF values
                  on the triplicate 12-lead electrocardiogram (ECG)] at baseline

          9. Hepatic function:

               1. Total bilirubin ≤ 1.5 x ULN, and

               2. AST ≤ 3 x ULN and ALT ≤ 3 x ULN

                    -  < 5 x ULN (if hepatic metastases)

        Exclusion Criteria:

          1. History or current evidence of another tumor that is histologically distinct from the
             tumor under study

          2. Current evidence of new or growing CNS metastases during screening

             -Subjects with known CNS metastases will be eligible if they meet specified criteria

          3. Evidence of CTCAE Grade >1 toxicity before the start of treatment, except for hair
             loss and those Grade 2 toxicities listed as permitted in other eligibility criteria

          4. History or evidence of significant cardiovascular disease

          5. Current evidence of active, uncontrolled hepatitis B virus, hepatitis C virus, human
             immunodeficiency virus (HIV) (evidenced by detectable viral load by PCR) or acquired
             immunodeficiency syndrome (AIDS) related illness

          6. Current evidence of ≥ grade 2 underlying pulmonary disease

          7. Certain exclusionary prior treatments