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

Inclusion Criteria

- Sign and date the main Informed Consent Form (ICF). - Has a left ventricular ejection fraction ≥50% by either an echocardiogram or multigated acquisition within 28 days of enrollment. - Has adequate organ function. - Measurable disease based on RECIST V1.1. - 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 - 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. - Is able to provide either of the following baseline tumor samples: - Fresh core needle biopsy samples obtained during the Screening Period, or - 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

- Has had prior treatment targeting mucin 1 (MUC1) or TA-MUC1. - Has spinal cord compression or history of/clinically active central nervous system metastases. - 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. - 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. - Has active human immunodeficiency virus (HIV) infection as determined by plasma HIV ribonucleic acid viral load and cluster of differentiation 4 count. - Has evidence of active hepatitis B virus or hepatitis C virus infection. - Any of the following within the past 6 months: cerebrovascular accident, transient ischemic attack, or other arterial thromboembolic event. - Has an active, known, or suspected autoimmune disease. - Current participation in other therapeutic investigational procedures, except for participation in Long Term Follow-Up without any investigational treatment.