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.