Trastuzumab deruxtecan (T-DXD) as monotherapy is indicated for the treatment of adult patients with advanced HER2-positive advanced gastric or gastroesophageal junction (GEJ) adenocarcinoma who have received a prior trastuzumab-based regimen.

This study will assess the effectiveness of T-DXd, patient demographic and clinical characteristics, and treatment patterns in patients with advanced HER2-positive advanced gastric or GEJ adenocarcinoma.

This non-interventional study will investigate the effectiveness of T-DXd, the patients demographic and clinical characteristics, treatment patterns including prophylactic medications and interventions for reduction of serious adverse events (SAEs), serious adverse drug reactions (ADRs) and safety event of interest (SEIs), tolerability, and patient survey of T-DXd, in cases with advanced HER2-positive gastric or GEJ adenocarcinoma receiving T-DXd as second line of treatment and beyond treatment option. Patients will be treated according to the proposed indication statement in the Summary of Product Characteristics (SmPC). No investigational drug will be administered in this study.

Data on conventional therapy (including platinum-fluoropyrimidine doublet chemotherapy, nivolumab, ramucirumab-paclitaxel, ramucirumab monotherapy, taxane or irinotecan, and pembrolizumab monotherapy) will also be collected in a disease registry part of the study.

Inclusion Criteria:

• 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 Informed Consent (ICF) to participate in the study

Exclusion Criteria:

• 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.

Adult patients with advanced HER2-positive gastric or GEJ adenocarcinoma who have received a prior trastuzumab-based regimen in a real-world setting in Europe.