A Study of DS-1471a In Subjects With Advanced Solid Tumors

Key Inclusion Criteria:

The clinical site will screen for the full inclusion criteria per protocol.

1. Sign and date the informed consent form (ICF)
2. Adults ≥18 years at the time the ICF is signed
3. Has a histologically or cytologically documented, locally advanced, metastatic, or unresectable solid tumor that is refractory to or intolerable with standard treatment, or for which no standard treatment is available
4. Has at least 1 measurable lesion according to RECIST v1.1
5. Is willing and able to provide fresh tumor tissue biopsied at Baseline (mandatory) and on-treatment (mandatory if clinically allowed and not contraindicated)
6. Eastern Cooperative Oncology Group performance status (ECOG PS) of 0 or 1
7. Life expectancy ≥3 months
8. Has a left ventricular ejection fraction (LVEF) ≥50% within 28 days prior to Cycle 1 Day 1
9. Required baseline local laboratory data (within 7 days prior to Cycle 1 Day 1) as prespecified in the protocol
10. If the participant is a female of childbearing potential, she must have a negative serum pregnancy test within 7 days prior to study drug administration (Cycle 1 Day 1) and must be willing to use highly effective birth control upon enrollment, during the Treatment Period, and for 7 months following the last dose of study drug
11. If male, the participant must be surgically sterile or willing to use highly effective birth control upon enrollment, during the Treatment Period, and for 4 months following the last dose of study drug
12. Is willing and able to comply with scheduled visits, study drug administration plan, laboratory tests, other study procedures, and study restrictions
13. Patients with liver cirrhosis and liver cancer may be eligible to participate if they meet additional protocol specified criteria

Key Exclusion Criteria:

The clinical site will screen for the full exclusion criteria per protocol.

1. Has an inadequate treatment washout period prior to start of study treatment (Cycle 1 Day 1) as prespecified in the protocol
2. Has history of or current presence of untreated central nervous system (CNS) metastases
3. Has a history of leptomeningeal carcinomatosis
4. Has a history of (non-infectious) interstitial lung disease (ILD) other than radiation pneumonitis, currently has ILD, or when suspected ILD cannot be ruled out by imaging at screening
5. Has a history of severe pulmonary compromise or requirement of supplemental oxygen within 6 months before enrollment
6. Has any of the following within the past 6 months: cerebrovascular accident, transient ischemic attack, arterial thromboembolic event, or pulmonary embolism
7. Has uncontrolled or clinically significant cardiovascular disease
8. Is requiring chronic steroid treatment (>10 mg daily prednisone equivalents)
9. Has multiple primary malignancies, except adequately resected non-melanoma skin cancer, curatively treated in situ disease, superficial cancer in the gastrointestinal tract curatively resected by endoscopic surgery, or any other solid tumors curatively treated with no evidence of recurrent disease for ≥3 years
10. Has unresolved toxicities from previous anticancer treatment
11. Exposure to another investigational medical product within 4 weeks prior to Cycle 1 Day 1 or current participation in other therapeutic investigational procedures
12. Has an active, known, or suspected autoimmune disease
13. Has evidence of ongoing uncontrolled systemic bacterial, fungal, or viral infection.
14. Has an active hepatitis or uncontrolled hepatitis B or C infection, except for HCC participants with hepatitis B infection that is controlled by antiviral therapy
15. Has human immunodeficiency virus (HIV) infection, with exceptions per protocol for participants in Dose Expansion
16. Has received a live, attenuated vaccine (messenger RNA [mRNA] and replication-deficient adenoviral vaccines are not considered live, attenuated vaccines) within 30 days prior to first exposure to study drug (Cycle 1 Day 1)
17. Female who is pregnant or breastfeeding or intends to become pregnant during the study
18. Has psychological, social, familial, or geographical factors that would prevent regular follow-up
19. Has prior or ongoing clinically relevant illness, medical condition, surgical history, physical finding, or laboratory abnormality that, in the investigator's opinion, could affect the safety of the subject; alter the absorption, distribution, metabolism, or excretion of the study drug; or confound the assessment of study results