A Study of Trastuzumab DeRuxtecan for Patients With Advanced HER2-pOsitive GaStric or GastroesoPhageal Junction AdEnocarcinoma Who Have Received a PrIor Trastuzumab-based Regimen Accompanied by a Disease RegistrY of Patients Treated With Conventional Therapies (PROSPERITY)

Who May Qualify: - Male or female adult patient (age ≥ 18 years) with HER2 + advanced gastric or GEJ adenocarcinoma who have received a prior trastuzumab based regimen - Histological or cytological confirmed diagnosis of advanced HER2 positive gastric cancer or GEJ - Documented HER2 + status (archival sample or recent sample prior 2L therapy) - Decision to newly initiate monotherapy T-DXd or conventional therapies per SMPC according to the physician's choice - Written dated and signed willing to sign a consent form (ICF) to participate in the study Who Should NOT Join This Trial: - Patients who at time of data collection for this study are participating in or have participated in an interventional study that remains blinded - Pregnancy or breastfeeding No specific exclusion criteria are defined, as patients will be treated according to the proposed indication statements in the SmPC. Always talk to your doctor about whether this trial is right for you.