• Institutions will be selected
• This study aims to collect real-world data, targeting patients who started treatment with Enhertu from September 2022, for clinical data collection
• Among patients treated with Enhertu, those who have passed away or are no longer visiting due to hospice care will have their clinical data collected without consent until August 19, 2024
• For patients who are scheduled to receive Enhertu treatment, are currently undergoing treatment, or have previously undergone treatment but experienced disease progression and are now receiving subsequent chemotherapy (i.e., patients with newly added data after registration)
• Efficacy evaluation

• Institutions will be selected through the Gastric Cancer Subcommittee of the Korean Cancer Study Group.
• This study aims to collect real-world data, targeting patients who started treatment with trastuzumab-deruxtecan from September 2022, for clinical data collection.
• Among patients treated with trastuzumab-deruxtecan, those who have passed away or are no longer visiting due to hospice care will have their clinical data collected without consent until August 19, 2024.
• For patients who are scheduled to receive Enhertu treatment, are currently undergoing treatment, or have previously undergone treatment but experienced disease progression and are now receiving subsequent chemotherapy (i.e., patients with newly added data after registration), data will be collected with consent until March 31, 2027.
• Efficacy evaluation will include overall survival (OS), progression-free survival (PFS), and tumor response rate (TRR)

Inclusion Criteria:

• Patients aged 19 years or older.
• Patients with pathologically confirmed metastatic, recurrent, or unresectable gastric/gastroesophageal adenocarcinoma.
• Patients whose tumor tissue shows HER2 immunohistochemistry (IHC) results of 3+ or 2+ with in-situ hybridization (ISH) positivity.
• Patients who received Trastuzumab Deruxtecan as third-line or later treatment.

Exclusion Criteria:

• Patients with HER2-negative gastric cancer.
• Patients who did not provide consent to participate in the study.
• Patients who received Trastuzumab Deruxtecan as first-line or second-line treatment as part of a clinical trial.

• Institutions will be selected
• targeting patients who started treatment with Enhertu from September 2022, for clinical data collection
• Among patients treated with Enhertu, those who have passed away or are no longer visiting due to hospice care will have their clinical data collected without consent until August 19, 2024.
• For patients who are scheduled to receive Enhertu treatment, are currently undergoing treatment, or have previously undergone treatment but experienced disease progression and are now receiving subsequent chemotherapy (i.e., patients with newly added data after registration), data will be collected with consent until March 31, 2027.
• Efficacy evaluation will include overall survival (OS), progression-free survival (PFS), and tumor response rate (TRR)