A Study of HER3-DXd in Subjects With Locally Advanced or Metastatic Solid Tumors

This is a proof-of-concept study designed to investigate HER3-DXd monotherapy in locally advanced unresectable or metastatic solid tumors. The study is enrolling cohorts of participants with melanoma \[cutaneous/acral\], squamous cell carcinomas of the head and neck (SCCHN), HER2-negative gastric cancer ovarian carcinoma, cervical cancer, endometrial cancer, bladder cancer, esophageal carcinoma, pancreatic carcinoma, prostate cancer, second-line gastric cancer, lung cancer, and breast cancer.

Inclusion Criteria Participants must meet all of the following criteria to be eligible for enrollment into the study: 1. Sign and date the informed consent form prior to the start of any study-specific qualification procedures. A separate tissue screening consent will be obtained from all subjects to meet the baseline tumor tissue requirement. 2. Participants aged ≥18 years (follow local regulatory requirements if the legal age of consent for study participation is \>18 years old). 3. Has locally advanced unresectable or metastatic disease (not curable by surgery or radiation) as follows: Cutaneous (acral and non-acral) melanoma 1. Histologically or cytologically confirmed cutaneous (acral or non-acral) melanoma 2. Disease progression while on or after having received treatment with ≥1 prior line of anti-programmed cell death protein (PD-1) or anti-programmed death-ligand 1 (PD-L1) based therapy (previous use of other immune checkpoint inhibitors \[ICIs\] \[ie, anti-CTLA4, anti- LAG-3\] is acceptable). Prior anti-PD-(L)1 therapy in the adjuvant setting is allowed if there is recurrence within 12 weeks of the last dose. If the participant had BRAFm melanoma, they must have had disease progression on BRAF/MEK inhibitor therapy as well. Squamous cell carcinomas of the head and neck 3. Squamous cell carcinoma of the head and neck (with a primary location of oral cavity,oropharynx, larynx, hypopharynx) that is human papillomavirus (HPV) positive or negative (as determined by local standard). Excludes tumor location in the nasopharynx, nasal cavity, paranasal sinuses, and unknown primary locations. 4. Disease progression after having received treatment with ≥1 and \