A Study of DS-9606a in Patients With Advanced Solid Tumors

Inclusion Criteria:

• 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 in Part A); patients withgerm cell tumors without archived tumor samples may be allowed with approval

• Has a left ventricular ejection fraction (LVEF) ≥50% as determined by either anechocardiogram (ECHO) or multigated acquisition scan (MUGA) within 28 days beforethe start of study treatment

• Adequate bone marrow and organ function within 7 days before the start of studytreatment

• 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 ofchild-bearing potential must agree to use a highly effective form of contraceptionor avoid intercourse during and upon completion of the study for at least 6 months (for males) and for at least 7 months (for females) after the last dose of studydrug. Males must agree not to freeze or donate sperm throughout the study period forat least 6 months after final administration of study drug. Investigators willadvise male patients on the conservation of sperm prior to study treatment. Femalesmust agree not to donate or retrieve ova for own use throughout the study period andfor 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 primaryperitoneal carcinoma), germ cell tumors, uterine and endometrial cancers, pancreaticadenocarcinoma, non-squamous NSCLC, or gastric cancer

• Disease progression with standard of care therapies for metastatic disease known toconfer benefit, or are intolerant to or refuse standard treatment.

Dose Expansion Participants Only:

• Consent to tumor screening and to provide an archived tumor sample if available, ora newly obtained pre-treatment tumor biopsy and consent to provide pre-treatmentbiopsy sample and on-treatment tissue biopsy sample (mandatory if not clinicallycontraindicated)

• Histologically or cytologically-documented locally advanced or metastatic ovariancancer

Exclusion Criteria:

• Has history or current presence of central nervous system metastases, except forparticipants who have completed radiotherapy or surgery ≥4 weeks before the start oftreatment, and fulfill all criteria (no evidence of disease progression in the CNSand no requirement for chronic corticosteroids) within 2 weeks before the start oftreatment

• Other invasive malignancy within 2 years; prior or concurrent non-invasivemalignancies and/or patients with localized malignancies that were treated withcurative intent who remain disease-free and are considered low likelihood forrecurrence may be enrolled

• History of myocardial infarction or unstable angina within 6 months before studytreatment

• Has a history of symptomatic congestive heart failure (New York Heart Associationclasses II-IV) or a serious cardiac arrhythmia requiring treatment

• Has a corrected QT interval by Fridericia's formula (QTcF), of >470 ms based on theaverage of triplicate 12-lead electrocardiogram (ECG) per local read

• Has a history of (non-infectious) interstitial lung disease (ILD)/pneumonitis thatrequired corticosteroids, current ILD/pneumonitis, or where suspectedILD/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