First-in-Human Study of DS-3939a in Participants With Advanced Solid Tumors

Inclusion Criteria:

1. Sign and date the main Informed Consent Form (ICF).
2. Has a left ventricular ejection fraction ≥50% by either an echocardiogram or multigated acquisition within 28 days of enrollment.
3. Has adequate organ function.
4. Measurable disease based on RECIST V1.1.
5. Eastern Cooperative Oncology Group performance status score of 0 or 1.

Additional inclusion criteria for Part 1

* Has a histologically or cytologically documented locally advanced, metastatic, or unresectable urothelial, non-small cell lung, breast, ovarian, or biliary tract cancers, or pancreatic ductal adenocarcinoma, regardless of any molecular subtypes.

Additional inclusion criteria for Part 2

1. Has a histologically or cytologically documented locally advanced, metastatic, or unresectable cancer meeting the protocol criteria and documented radiographic disease progression during or after the most recent anticancer therapy.
2. Is able to provide either of the following baseline tumor samples:

1. Fresh core needle biopsy samples obtained during the Screening Period, or
2. Alternative FFPE tumor tissue samples obtained by biopsy or surgery performed after the completion date of the most recent anticancer therapy regimen and within 6 months before signing the ICF

Exclusion Criteria:

1. Has had prior treatment targeting mucin 1 (MUC1) or TA-MUC1.
2. Has spinal cord compression or history of/clinically active central nervous system metastases.
3. Has multiple primary malignancies, except adequately resected nonmelanoma skin cancer, curatively treated in situ disease, or other solid tumors curatively treated, with no evidence of disease for ≥3 years.
4. Has a history of noninfectious interstitial lung disease (ILD)/pneumonitis (including suspected one), has current ILD/pneumonitis, or where suspected ILD/pneumonitis cannot be ruled out by imaging at Screening.
5. Has active human immunodeficiency virus (HIV) infection as determined by plasma HIV ribonucleic acid viral load and cluster of differentiation 4 count.
6. Has evidence of active hepatitis B virus or hepatitis C virus infection.
7. Any of the following within the past 6 months: cerebrovascular accident, transient ischemic attack, or other arterial thromboembolic event.
8. Has an active, known, or suspected autoimmune disease.
9. Current participation in other therapeutic investigational procedures, except for participation in Long Term Follow-Up without any investigational treatment.