Objective Sleep Characteristics and Neoadjuvant Immunotherapy Response in Gastric/GEJ Cancer

This prospective observational study will enroll 120 patients with locally advanced gastric or gastroesophageal junction adenocarcinoma who are scheduled to receive neoadjuvant immunotherapy followed by radical surgery. Non-invasive objective sleep monitoring will be performed during the neoadjuvant treatment period to assess sleep characteristics, including sleep duration, sleep efficiency, device-estimated deep sleep proportion, nocturnal awakenings, sleep regularity, heart rate, and heart rate variability. The primary objective is to evaluate the association between objective sleep characteristics and major pathological response (MPR) after neoadjuvant immunotherapy. This study will not alter standard treatment decisions, surgical procedures, or perioperative management.