Experimental: Laparoscopic proximal gastrectomy Laparoscopy proximal gastrectomy with esophago-jejunostomy, gastro-jejunostomy and jejuno-jejunostomy (double tract reconstruction). Systemic en bloc lymph node dissection is mandatory. Resection margin should be negative for malignancy with intraoperative frozen biopsy.

Active Comparator: Laparoscopic total gastrectomy Laparoscopic total gastrectomy with esophago-jejunostomy and jejuno-jejunostomy (Roux-en-Y reconstruction). Systemic en bloc lymph node dissection is mandatory. Resection margin should be negative for malignancy with intraoperative frozen biopsy.

Participating Surgeons Prior to this clinical trial, only the surgeons who are considered to have the standardization by review committee participated.

Patients Registration It is required to ensure that the patients meet the inclusion criteria for this clinical trial, are free from any items of exclusion criteria, are explained about the participation in the clinical trial along with the informed consent forms.

After rechecking the patients with the registration check list by accessing the web-based randomized program provided from Seoul National University Bundang Hospital Medical Research Collaborating Center.

Each group 69 patients, total 138 subjects will be enrolled. Randomization The registration randomization should be done with 1:1 ratio for each researcher.

Baseline number (BN) should be provided to the subjects in the order of acquisition of informed consent form. Based on the subjects who are selected as the appropriate subjects in the end, the allocation number (AN) shall be provided in the order of randomized allocation table.

Procedure Operations are performed according to the allocated group.

Inclusion Criteria:

• Patients are included in the trial if they meet all of the following criteria:

Histologically proven adenocarcinoma through endoscopic biopsy Aged 20-80 years old Written signed informed consent No other malignancies Proximal gastric cancer met by following conditions ; Lesion located on proximal stomach (upper one third) Lesion below 5cm in size Lesion confined to mucosa or submucosa (cT1) No evidence of metastatic enlarged LN on #5, 6, 4d, 10 basins and other distant metastasis.

Performance status (PS) of 0 or 1 on Eastern Cooperative Oncology Group (ECOG) scale Performance status (PS) of I to III on American Society of Anesthesiologists (ASA) score

Exclusion Criteria:

• Patients are excluded if they meet any of the following criteria:

History of anemia Patients who need total gastrectomy History of pre-operative chemotherapy or radiation therapy for gastric cancer Patients who need combined resection (except cholecystectomy) Presence of other malignancies Prior treatment against systemic inflammatory disease Previous gastric surgery Vulnerable patients (lack of decision-making capacity, pregnant, or breast-feeding women)