Metastatic Exophytic Gastric Adenocarcinoma Diagnosed Using Endoscopic Ultrasound-Guided Fine-Needle Biopsy: A Case Report

A 75-year-old female patient presented to our department with abdominal distension for the past month. Physical examination revealed abdominal distension without tenderness. Carcinoembryonic antigen, carbohydrate antigen 19-9, and cancer antigen 125 levels were 4.2 ng/mL, 125.8 U/mL, and 8,423.9 U/mL, respectively. Contrast-enhanced computed tomography displayed a 110-mm-sized exophytic gastric tumor. The tumor was accompanied by ascites but without lymph node enlargement. Esophagogastroduodenoscopy revealed extrinsic compression in the posterior wall of the gastric fundus. The surface was completely covered with normal mucosa, and endoscopic forceps biopsy exhibited no abnormal findings. The cytodiagnosis of ascites obtained by abdominal paracentesis revealed adenocarcinoma. Endoscopic ultrasonography revealed that the exophytic gastric tumor was uniformly hypoechoic, and a fine-needle biopsy was performed. The histopathological finding revealed adenocarcinoma. Immunohistochemical analysis showed that these cells expressed cytokeratin 7 but not cytokeratin 20, CD117, CD34, chromogranin A, and synaptophysin, confirming the diagnosis of exophytic gastric adenocarcinoma with peritoneal dissemination. The tumor was mismatch repair proficient and did not express claudin-18.2 and human epidermal growth factor receptor 2. Programmed death-ligand 1 combined positive score was <10. Based on the results of genetic expression, chemotherapy comprised of tegafur-gimeracil-oteracil potassium, oxaliplatin and nivolumab was considered; however, the patient rapidly deteriorated and died of progression of underlying cancer 39 days following the initial visit to our hospital.