Gastric Adenocarcinoma Resembling Submucosal Tumor: A Case Report

BACKGROUND Gastric cancer with features of submucosal tumor (GCSMT) is extremely rare and often manifested as poorly differentiated or undifferentiated types, including poorly differentiated adenocarcinoma and gastric signet ring cell carcinoma, which are more invasive. Because a GCSMT is almost covered by normal mucosa, it is difficult to diagnose by gastroscopy and easy to misdiagnose as a benign submucosal tumor (SMT). We report a case of poorly differentiated gastric adenocarcinoma exhibiting the features of a SMT. CASE REPORT The patient was a 60-year-old man with a chief concern of stomach discomfort for nearly 2 months. Gastroscopy revealed a lesion located at the lesser curvature of the stomach. Endoscopic ultrasonography displayed a 2.0×0.8-cm, well-defined, hypoechoic mass arising from the muscular layer in the stomach wall, suggesting a gastrointestinal stromal tumor (GIST). However, pathologic examination of the specimen removed by endoscopic submucosal dissection (ESD) demonstrated poorly differentiated adenocarcinoma. Therefore, subtotal gastrectomy with lymph node dissection was performed. CONCLUSIONS Based on our clinical experience, the tumor had the typical characteristics of a GIST in gastroscopy and abdominal computed tomography and was considered to be a GIST. However, the pathological examination revealed poorly differentiated gastric cancer, thereby demonstrating the importance of pathology in making final diagnoses in clinical practice. Clinicians often prioritize a diagnosis of GIST in similar cases of SMT; however, the possibility of gastric cancer should also be considered. Additionally, for SMTs of unclear nature, ESD serves as treatment and provides biopsy tissue for definitive pathological diagnosis.