A Phase 1, First-in-Human Study of DS-9606a in Patients with Tumor Types Known to Express Claudin-6 (CLDN6)

• At least 18 years old at the time of written informed consent
• Eastern Cooperative Oncology Group (ECOG) Performance Status score of 0 or 1
• Availability of archived tumor tissue samples (mandatory); patients with germ cell tumors without archived tumor samples may be allowed with approval
• Has a left ventricular ejection fraction (LVEF) ≥50% as determined by either an echocardiogram (ECHO) or multigated acquisition scan (MUGA) within 28 days before the start of study treatment
• Adequate bone marrow and organ function within 7 days before the start of study treatment
• Life expectancy ≥3 months
• Adequate treatment washout period prior to start of study treatment
• Male patients with female partners of childbearing potential and female patients of child-bearing potential must agree to use a highly effective form of contraception or avoid intercourse during and upon completion of the study for at least 4 months (for males) and for at least 7 months (for females) after the last dose of study drug. Males must agree not to freeze or donate sperm throughout the study period for at least 4 months after final administration of study drug. Females must agree not to donate or retrieve ova for own use throughout the study period and for at least 7 months after final study drug administration.

Dose Escalation Participants Only:

• Histologically- or cytologically-documented locally advanced or metastatic cancers, including but not limited to: ovarian cancer (including fallopian tube and primary peritoneal carcinoma), germ cell tumors, uterine and endometrial cancers, pancreatic adenocarcinoma, non-squamous NSCLC, or gastric cancer
• Disease progression with standard of care therapies for metastatic disease known to confer benefit, or are intolerant to or refuse standard treatment.

Dose Expansion Participants Only:

• Consent to provide pre-treatment (mandatory) and on-treatment tissue biopsy sample (mandatory if not clinically contraindicated)
• Histologically or cytologically-documented locally advanced or metastatic cancers including:
• Cohort B-1: Ovarian cancer
• Cohort B-2: Refractory germ cell tumors

• Has history or current presence of central nervous system metastases, except for participants who have completed radiotherapy or surgery ≥4 weeks before the start of treatment, and fulfill all criteria (no evidence of disease progression in the CNS and no requirement for chronic corticosteroids) within 2 weeks before the start of treatment
• Other invasive malignancy within 2 years; prior or concurrent non-invasive malignancies and/or patients with localized malignancies that were treated with curative intent who remain disease-free and are considered low likelihood for recurrence may be enrolled
• History of myocardial infarction or unstable angina within 6 months before study treatment
• Has a history of symptomatic congestive heart failure (New York Heart Association classes II-IV) or a serious cardiac arrhythmia requiring treatment
• Has a corrected QT interval by Fridericia's formula (QTcF), of >470 ms based on the average of triplicate 12-lead electrocardiogram (ECG) per local read
• Has a history of (non-infectious) interstitial lung disease (ILD)/pneumonitis that required corticosteroids, current ILD/pneumonitis, or where suspected ILD/pneumonitis cannot be ruled out by imaging at screening.
• Has an uncontrolled infection requiring ongoing or long-term therapy
• Has a known active hepatitis or uncontrolled hepatitis B or C infection