A Study Evaluating DS-1055a in Participants With Relapsed or Refractory Locally Advanced or Metastatic Solid Tumors

Inclusion Criteria:

• Has a histopathologically documented locally advanced or metastatic head and neck,gastric, esophageal cancer, non-small cell lung cancer, or melanoma. Participantswith other types of solid tumors may be eligible following discussion with theSponsor.

• Has a relapsed or refractory disease that is not amenable to curative standardtherapy.

• Is 18 years of age or older.

• Has an Eastern Cooperative Oncology Group Performance Status (ECOG PS) of 0-1, withno deterioration for two weeks.

• Has a measurable disease based on Response Evaluation Criteria in Solid Tumors (RECIST) version 1.1.

• Has adequate organ function within 7 days before enrollment.

• Is able to provide written informed consent and is willing and able to comply withthe protocol.

Exclusion Criteria:

• Has a concurrently active second malignancy, other than adequately treatednon-melanoma skin cancers, in situ melanoma or in situ cervical cancer. Participantswith history of the second malignancy have been disease-free for <3 years.

• Has a history of (non-infectious) interstitial lung disease (ILD) that requiredsteroids, currently has ILD, or when suspected ILD cannot be ruled out by imaging atscreening.

• Has a history of severe pulmonary compromise or requirement of supplemental oxygenwithin 6 months before enrollment.

• Has active hepatitis B or hepatitis C virus infection.

• Has received prior immunotherapy with a Grade 3 or higher, or any unresolved ≥Grade 2 immune-related adverse event.