ERBB2 and esophageal adenocarcinoma: Part 4 evaluates T-DXd 5.4 mg/kg in combination with rilvegostomig, a PD-1/T-cell immunoreceptor with Ig and ITIM domains (TIGIT) bispecific antibody, and a fluoropyrimidine (5-FU or CAPE) in patients with HER2+ or HER2-low gastric, GEJA, or esophageal adenocarcinoma.