SPADE Clinical Trial.

* Inclusion Criteria ① Histologically confirmed diagnosis of gastric adenocarcinoma by biopsy. * Adult patients aged 20 years or older. * Eastern Cooperative Oncology Group (ECOG) performance status of 0 to 2. ④ American Society of Anesthesiologists (ASA) physical status classification of class I to III. ⑤ Patients who have received a full explanation of the study purpose and procedures, and voluntarily signed the informed consent form approved by the Institutional Review Board. ⑥ Patients eligible for proximal gastrectomy satisfying the following oncologic characteristics on preoperative evaluation: • Tumor location: Upper third of the stomach (High body, cardia, fundus, gastroesophageal junction \[Siewert III\]) * Tumor size: 4 cm or less * Preoperative clinical stage: T1N0, T1N1, T2N0, T2N1 (any differentiation) * Preoperative clinical stage: T3N0, T3N1 (well or moderate differentiation) * Expected residual stomach: 60% or more after surgery * Exclusion Criteria * Patients for whom total gastrectomy is the only appropriate treatment (e.g., presence of additional gastric cancer lesions in the distal stomach). ② Patients requiring concomitant resection of other organs due to other diseases. ③ Patients with other malignancies that may affect gastric function preservation indicators: • History of cancer in other organs. * Presence of concurrent cancer in other organs. * History of previous gastric resection surgery. ④ Vulnerable populations: patients lacking decision-making capacity, pregnant women, or those planning pregnancy.