The article describes the case of a 69-year-old man who underwent radical gastrectomy (removal of the stomach) for esophageal junction cancer with a diagnosis of diffuse infiltrative mucinous adenocarcinoma with components of signet-ring cell carcinoma and neuroendocrine carcinoma. The patient received six cycles of adjuvant chemotherapy with S-1 and oxaliplatin, and no evidence of recurrence was detected during routine follow-up. Twenty-one months after surgery, he developed left upper abdominal pain, and computed tomography revealed a solitary metastasis in the left adrenal gland. Ultrasound-guided biopsy confirmed metastatic gastric adenocarcinoma, and tumor markers (CA72-4, CA19-9, and carcinoembryonic antigen) were significantly elevated. The patient was treated with SOX chemotherapy combined with the PD-1 inhibitor tislelizumab, and his overall condition improved after the first treatment cycle. The case highlights the need for vigilance for rare adrenal metastases in patients with advanced gastric cancer even after standardized postoperative follow-up, and suggests that systemic chemotherapy combined with immunotherapy may be an effective treatment strategy.