• Age: ≥18 years

• Has a life expectancy of ≥3 months

• Has documented locally advanced or metastatic HER2expressing (IHC 1+ to 3+ and/or HER2 gene amplification or activating mutation in tumor specimen by ISH or NGS) solid tumor(s) not amenable to curative surgery or radiation and has received at least 2 lines of standard therapy, including adjuvant/neoadjuvant treatment, or whose cancer is considered refractory to the standard of care or for which no standard treatment is available, including:

∙ Cohort 1: Subjects with HER2 expression in endometrial cancers (EC)

‣ Cohort 2: Subjects with HER2 expression in cervical cancers (CC)

‣ Cohort 3: Subjects with HER2 expression in ovarian cancers (OC) including fallopian tube cancer and primary peritoneal cancer

‣ Cohort 4: Subjects with HER2 expression in urothelial cancers (UC)

‣ Cohort 5: Subjects with HER2 expression in biliary tract cancers (BTC)

‣ Cohort 6: Subjects with HER2 expression in breast cancer (BC)

‣ Cohort 7: Subjects with HER2 expression in lung cancer (LC)

‣ Cohort 8: Subjects with HER2 expression in gastric, esophageal, or gastroesophageal junction (GEJ) cancers

• Agree to provide most recent existing tumor samples (FFPE tissue block or slides) from primary or metastatic sites for tissue-based IHC staining to centrally determine HER2 expression:

∙ In dose escalation and dose finding: archival tissue or fresh biopsy. If no archival tissue is available, or it is not possible to obtain a fresh tissue biopsy, medical monitor approval is required to screen subject;

‣ In dose expansion: an FFPE block or slides from fresh biopsy or the most recent archival tissue is required.

• Has at least one measurable lesion based on RECIST (Response Evaluation Criteria in Solid Tumors) V1.1

• Has an Eastern Cooperative Oncology Group performance status (ECOG PS) of 0 to 1

• Toxicity of previous antitumor therapy has returned to Grade ≤1

• Has no serious cardiac dysfunction, left ventricular ejection fraction ≥50%

• Has adequate organ function before enrollment, defined as:

⁃ Coagulation function: international normalized ratio (INR) ≤1.5×ULN, and activated partial thromboplastin time (APTT) ≤1.5 ULN, unless receiving anticoagulation therapy with prothrombin time and aPTT levels within the intended therapeutic range

⁃ Urinary protein ≤2+ or ≤1000 mg/24 hours

⁃ For premenopausal women with childbearing potential, a pregnancy test must be taken within 7 days prior to the start of treatment. Serum or urine pregnancy test must be negative and subject must be nonlactating.

⁃ Must agree to use adequate contraceptive measures during the treatment and for 6 months after the end of treatment for all subjects (regardless of gender)