This is a single-center, prospective observational cohort study designed to evaluate the association between pretreatment emotional distress and pathologic response to perioperative immunotherapy in patients with locally advanced gastric or gastroesophageal junction adenocarcinoma. A total of 120 patients planned for neoadjuvant immunotherapy followed by curative surgery will be enrolled. Emotional distress will be assessed using the PHQ-9 and GAD-7 before treatment initiation and at prespecified time points during treatment. Participants will be classified into an emotional distress group or a non-emotional distress group according to predefined criteria. The primary endpoint is major pathological response (MPR). Secondary endpoints include pathological complete response (pCR), R0 resection rate, event-free survival (EFS), recurrence-free survival (RFS), and overall survival (OS). Exploratory analyses will assess dynamic changes in emotional distress and their associations with peripheral stress markers, peripheral immune markers, and tumor immune microenvironment features.

Inclusion Criteria:

1. Willing to participate in this study.
2. Age >18 years; both sexes are eligible.
3. Histologically confirmed gastric adenocarcinoma or gastroesophageal junction adenocarcinoma.
4. Resectable locally advanced disease as assessed by imaging and/or multidisciplinary team evaluation, generally corresponding to AJCC 8th edition stage II-III disease, including cT3-4a with any N category or any T with node-positive disease, without distant metastasis.
5. Planned to receive neoadjuvant therapy followed by curative-intent surgery.
6. Eastern Cooperative Oncology Group (ECOG) performance status of 0-1.
7. No prior systemic antitumor treatment for the current tumor at baseline.
8. Able to understand and complete questionnaire assessments.
9. Able and willing to provide written informed consent.

Exclusion Criteria:

1. Presence of distant metastasis, peritoneal metastasis, or loss of curative treatment opportunity as determined by clinical evaluation.
2. Prior neoadjuvant chemotherapy, immunotherapy, radiotherapy, or other systemic antitumor treatment for the current tumor.
3. Severe cognitive impairment, acute psychiatric disorder, or any condition that precludes completion of questionnaire assessments.
4. Current treatment with antidepressants, anxiolytics, or other psychotropic medications with any of the following within 4 weeks before baseline assessment: initiation, discontinuation, change in medication type, dose adjustment of 50% or more, or addition of a second or more psychotropic medication.
5. Any other condition judged by the investigator to make the participant unsuitable for enrollment.

Adults with histologically confirmed, resectable, locally advanced gastric or gastroesophageal junction adenocarcinoma who are planned to receive neoadjuvant/perioperative immunotherapy followed by curative-intent surgery at West China Hospital. Eligible participants must have stage II-III disease without distant metastasis, an ECOG performance status of 0-1, no prior systemic antitumor treatment for the current tumor at baseline, and the ability to complete questionnaire assessments before and during treatment.