Ph1b/2 Study of the Safety and Efficacy of T-DXd Combinations in Advanced HER2-expressing Gastric Cancer (DESTINY-Gastric03)

Inclusion Criteria

• Male and female participants must be at least 18 years of age. Other age restrictions may apply as per local regulations
• Disease Characteristics:
• Locally advanced, unresectable, or metastatic disease based on most recent imaging
• For Part 1, 2, 3a, 4a pathologically documented adenocarcinoma of the stomach/GEJ/esophagus, HER2-positive (IHC 3+ or IHC 2+/ISH+) based on local tissue testing results
• For Part 3b and 4b, pathologically documented adenocarcinoma of the stomach/GEJ/esophagus, HER2-low (IHC 2+/ISH-negative or IHC 1+) based on local tissue testing results
• For Part 1, progression on or after at least one prior trastuzumabcontaining regimen For Part 2, Part 3 and Part 4, previously untreated for unresectable or metastatic adenocarcinoma of the stomach/GEJ/ esophagus with with HER2-positive (Part 2 and Part 3 [Arm 3A] and Part 4 [Arm 4A]) or HER2-low (Part 3 [Arm 3B] and Part 4 [Arm 4B])) status
• Has measurable target disease assessed by the Investigator based on RECIST version 1.1
• Has protocol defined adequate bone marrow and organ function including cardiac, renal and hepatic function
• If of reproductive potential, agrees to use a highly effective form of contraception or avoid intercourse during and upon completion of the study.

Exclusion Criteria

• History of active primary immunodeficiency, known HIV, active chronic, or past hepatitis B infection, or hepatitis C infection.
• Uncontrolled intercurrent illness
• History of non-infectious pneumonitis/ILD, current ILD, or where suspected ILD that cannot be ruled out by imaging at screening.
• Lung-specific intercurrent clinically significant severe illnesses.
• Uncontrolled infection requiring intravenous (IV) antibiotics, antivirals, or antifungals.
• Pleural effusion, ascites or pericardial effusion that requires drainage, peritoneal shunt, or Cell-free and Concentrated Ascites Reinfusion Therapy (CART).
• Has spinal cord compression or clinically active central nervous system metastases.