A 32-year-old man with dyspeptic symptoms underwent an upper gastrointestinal endoscopy at a local clinic, which revealed abnormal findings; he was subsequently referred to our hospital for further evaluation. Esophagogastroduodenoscopy demonstrated an ulcerative lesion characterized by a thick whitish exudate on the ulcer base with an uneven surface at anterior wall of upper body. The periphery of the ulcer exhibited a soft, elevated margin resembling the contour of the auricle and several submucosal elevations covered with intact mucosa were noted alongside the ulcerative lesion (Fig. 1). Histopathological examination revealed only inflammatory cell infiltration without evidence of malignancy. Abdominopelvic computed tomography revealed large, heterogeneously enhancing conglomerate masses exceeding 20 cm in the central abdomen, with invasion into the stomach and omentum. And peritoneal carcinomatosis with a small amount of ascites, multiple hepatic metastases (up to 2 cm in size), and suspected metastatic lymphadenopathy around the celiac axis were also found (Fig. 2). What are the possible differential diagnoses, and what additional investigations are warranted for definitive diagnosis?

On initial endoscopy, the lesion appeared as an auricle-like ulcerative mass, which raised suspicion for gastric lymphoma. Nevertheless, biopsy findings were not consistent with lymphoma. In light of the CT findings showing a large mass arising from the gastric wall, differential diagnoses included a malignant gastrointestinal stromal tumor (GIST) of gastric or omental origin, or an advanced gastric carcinoma with diffuse omental involvement, with or without regional lymph node metastasis. To achieve an accurate diagnosis and debulk the tumor burden, surgical resection was undertaken. Histopathological analysis of the resected specimens, including the stomach (subtotal gastrectomy), jejunum and cecum (segmental resection), and omentum (omentectomy), revealed a GIST, epithelioid variant (Fig. 3). On immunohistochemical staining, the tumor cells were positive for c-KIT and DOG1, while CK, CD20, CD79a, Bcl-2, CD3, synaptophysin, and CD1a were all negative. The Ki-67 labeling index was 8% (Fig. 4). The tumor measured 23×23 cm in size and extended from the gastric fundus to the body. The mitotic count was 3 per 5 mm². Extensive lymphovascular invasion was observed, while perineural invasion was absent. Metastatic involvement was identified in 4 of 13 regional lymph nodes (Fig. 5). Resection margins were clear. Multiple metastatic GIST lesions were also identified in the peritoneum, omentum, gallbladder (involving the serosal surface), and appendix (serosal involvement). Postoperatively, the patient was started on imatinib and later transitioned to sunitinib.

GISTs are mesenchymal neoplasms that arise primarily in the gastrointestinal tract and peritoneum. Although relatively rare compared to adenocarcinomas, GISTs are the most common type of sarcoma originating in the gastrointestinal tract and account for approximately 5% of all sarcomas [1]. In 1998, Hirota et al. [2] from Japan demonstrated that constitutive activation of the KIT protein due to mutations in the KIT gene is a key pathogenic mechanism of GISTs. Subsequently, muta-tions in the PDGFRA gene were also identified as another oncogenic driver in GISTs [3]. The annual incidence of GISTs is estimated to be 10–20 cases per million population. Approximately 20%–30% of all GISTs exhibit clinically malignant behavior [4]. GISTs are often detected incidentally in asymptomatic patients. This is primarily because GISTs arise within the abdominal cavity and originate from the muscularis propria rather than the mucosal layer of the gastrointestinal tract, allowing them to grow to a considerable size before causing symptoms. In contrast, when the tumor enlarges significantly, clinical manifestations may develop. Patients may present with a palpable abdominal mass or abdominal pain. If the tumor grows intraluminally, it may cause bowel obstruction [1].

Histological confirmation prior to treatment is essential in the management of GISTs. However, in the present case, endoscopic biopsy failed to establish a diagnosis. Although endoscopic ultrasound-guided fine-needle biopsy could be considered, surgical resection was preferred in order to achieve mass reduction and symptomatic relief. Therefore, primary surgical resection was performed in this case. The patient in this case was younger than the typical age range for GISTs, which most commonly occur in individuals in their 50s to 60s. He was also younger than the recommended starting age for upper gastrointestinal endoscopy in Korea’s national cancer screening program. Given that small GISTs are often asymptomatic, it is likely that the diagnosis was delayed due to the tumor remaining clinically silent until it reached a considerable size.