This study aims to evaluate the tumor deposit at the fusion site of the right gastric mesentery and left gastric mesentery in the patients with gastric cancer who received proximal gastrectomy.

In the 6th edition of the Japanese Gastric Cancer Treatment Guidelines; during proximal gastrectomy, D2 lymphadenectomy includes nodes No. 1, No. 2, No. 3a, No. 4sa, No. 4sb, No. 7, No. 8a, No. 9, No. 11p, and No. 11d. When performing D2 surgery for proximal gastric cancer, the dissection typically includes No. 3a (Lymph nodes along the branches of the left gastric artery, including those below the cardia branch) and No. 7 (distributed along the left gastric artery from its root to the bifurcation of the ascending branch), while not including the No. 5 group nodes (located in the upper region of the pylorus between the root of the right gastric artery and the first branch of the gastric wall). In D2 lymphadenectomy plus complete mesogastric excision (CME) for proximal gastric cancer, a complete resection of the left gastric mesentery is performed without removing the right gastric mesentery. However, clinical observations have shown that there may be a fusion between the left and right gastric mesenteries. Merely excising the left gastric mesentery could potentially lead to tumor residue or recurrence in the right mesentery. This study aims to investigate tumor deposit at the fusion site of the right gastric mesentery and left gastric mesentery following D2+CME surgery for proximal gastric cancer, intending to provide evidence-based medical insights for standardizing lymph node clearance in gastric cancer.

Inclusion Criteria:

1. Aged older than 18 years and younger than 85 years
2. Primary gastric adenocarcinoma confirmed by preoperative pathology result
3. cT2-4aN0-3M0 at preoperative evaluation according to the American Joint 8 Committee on Cancer (AJCC) Cancer Staging Manual 8th Edition
4. Patients undergoing proximal gastrectomy with D2 lymphadenectomy plus complete mesogastric excision
5. American Society of Anesthesiologists (ASA) class I, II, or III
6. Written informed consent

Exclusion Criteria:

1. Negative preoperative biopsy
2. Too late tumour stage or metastasis (cT4b/M1)
3. BMI>30 kg/m2
4. previous neoadjuvant chemotherapy or radiotherapy
5. Previous upper abdominal surgery
6. Combined with other malignant diseases
7. Reject operation

Patients undergoing proximal gastrectomy with D2 lymphadenectomy plus complete mesogastric excision. At the same time, the patients met the above inclusion and exclusion criteria.