Study of ADCT-502 in Patients With Advanced Solid Tumors Withhuman Epidermal Growth Factor Receptor-2 (HER2) Expression

Main Inclusion Criteria:

* Male or female age 18 years or older
* Refractory to or intolerant of existing therapy(ies) known to provide clinical benefit for their condition.
* Eastern Cooperative Oncology Group (ECOG) performance status: Part 1: 0-2, Part 2: 0-1
* Availability of formalin-fixed paraffin-embedded (FFPE) tumor tissue block or unstained slides to demonstrate HER2 expression.
* Pathologic diagnosis of solid tumor malignancy that is locally advanced or metastatic at time of Screening with documented HER2 expression.
* Part 2/Dose Expansion Only: Measurable disease as defined by Response Evaluation Criteria in Solid Tumors (RECIST) version 1.1
* Absolute neutrophil count (ANC) ≥ 1500/mm3 (≥1.5× 109/L).
* Platelet count ≥100,000 //mm3 (≥100 × 109/L).
* Hemoglobin ≥ 9 g/L (≥5.6 mmol/L).
* Aspartate transaminase (AST) and alanine aminotransferase (ALT) ≤ 2.5 x upper limit of normal (ULN); or ≤ 5.0 × ULN if liver metastases are present.
* Total bilirubin ≤ 1.5× ULN (or ≤ 3× ULN, with direct bilirubin ≤1.5 × ULN, in participants with known Gilbert syndrome).
* Creatinine ≤ 1.5× ULN; or, if serum creatinine \> 1.5 × ULN, a measured creatinine clearance must be \>60mL/min/1.73m2 as calculated by the Cockcroft and Gault equation for participants to be eligible.
* Women of childbearing potential must agree to use a highly effective method of contraception from the time of giving informed consent until at least 16 weeks after the last dose of ADCT-502. Men with female partners who are of childbearing potential must agree that they or their partners will use a highly effective method of contraception from the time of giving informed consent until at least 16 weeks after the participant receives his last dose of ADCT-502.

Main Exclusion Criteria:

* Known history of ≥ Grade 3 hypersensitivity to a therapeutic antibody.
* Known history of positive serum human anti-drug antibody (ADA) to trastuzumab.
* Major surgical procedure or significant traumatic injury, radiotherapy, chemotherapy, targeted therapy, hormone therapy, or other anticancer therapy.
* Failure to recover to Grade 0 or Grade 1 from acute non-hematologic toxicity due to previous therapy, prior to screening (with the exception of alopecia).
* Central Nervous System (CNS) disease only.
* Symptomatic CNS metastases or evidence of leptomeningeal disease.
* Active cardiovascular disease or significant history thereof.
* Other active disease including but not limited to ulceration of the upper gastrointestinal tract, autoimmune disease, HIV infection, active Hepatitis B virus (HBV) and hepatitis C virus (HCV) infection.
* Breastfeeding or pregnant.
* Other concurrent severe and/or uncontrolled medical conditions.