Real-World Observational Study to Describe Treatment Patterns in Patients With HER2-Positive Locally Advanced or Metastatic Gastric or Gastroesophageal Junction Cancer in East Asia

Inclusion Criteria: * Adult participants at the time of 1st LOT (Index Date 1e) initiation - Adult patients ≥18 years old. (Please follow local regulatory requirements if the legal age of consent for study participation is \>18 years old.) * Participants or next of kin/legal representatives who are willing to provide written informed consent as per the local regulations (if IRB/IEC/EC grants a permission to waive informed consent, it is not necessary). * Participants who were pathologically and/or clinically diagnosed with locally advanced or metastatic gastric or gastroesophageal adenocarcinoma (de novo advanced disease, relapsed/progressed) since January 1, 2016, and its record is available at the study participating site. * Participants whose HER2 status were pathologically confirmed HER2-positive (IHC3+ or IHC2+/ISH-positive) before/at the Index Date 2f based on the most recent archived tumor tissue sample to the Date of Diagnosisg, and its record is available at the study participating site. * Participants who received at least 1 LOT for HER2-positive locally advanced or mGC/GEJC in an advanced setting, and its record is available at study participating site. Trastuzumab or its biosimilar use is not required. °Progression on or within 6 months post neoadjuvant or adjuvant therapy is counted as "rapid progressor" in a neo-adjuvant/adjuvant setting, and thus equivalent to advanced/metastatic disease failing 1 LOT. * Participants who have at least 6 months of follow-up data from the date of 2nd LOT initiation (Index Date 2f) unless participant died within the first 6 months from the Index Date 2, and its record is available at the study participating site. * For rapid progressor participants in a neo-adjuvant/adjuvant setting, "Index Date 1" will be the date of neo-adjuvant treatment initiation or adjuvant treatment initiation. Exclusion Criteria: * Participants with a change in HER2 status from positive to negative at progression from early-stage to advanced-stage disease (change from HER2-positive to HER2-negative on repeat biopsy during treatment for advanced stage can be participated). However, if HER2-positive was confirmed before the Date of Diagnosis (or if HER2-positive was confirmed using an archived tumor tissue sample collected during early stage) and the result was followed to make the decision for the 1st LOT, this is not the case. * Participants who had multiple cancer within 3 years of 1st LOT initiation (Index Date 1), except adequately resected melanoma skin cancer, curatively treated in-situ disease, other solid tumors curatively treated. * Participants who are participating or have participated in an interventional study that remains blinded at time of informed consent (IC) or at the time of data collection for participants whose IC is waived by the local IRB/EC/IEC.