A Case of Gastric Atypical Lipomatous Tumor/Well‐Differentiated Liposarcoma With Endoscopic Morphological Changes

Atypical lipomatous tumor/well-differentiated liposarcoma is a locally aggressive mesenchymal neoplasm composed of adipocytes and stromal cells. Gastric cases are exceedingly rare, and their malignant potential remains unclear. We report a case of a woman in her 60s who was found to have multiple submucosal tumor-like lesions of the stomach. Over time, the tumors increased in size, requiring a laparoscopic partial gastrectomy. Histological examination revealed a tumor composed of both fatty tissue and fibrous stroma with nuclear atypia. Immunohistochemistry showed positivity for CDK4 and MDM2, and fluorescence in situ hybridization confirmed <i>MDM2</i> amplification, leading to a diagnosis of atypical lipomatous tumor/well-differentiated liposarcoma. This case presented an unusual gastric manifestation, with multiple submucosal tumor-like lesions on endoscopy and exhibiting progressive morphological changes over several years.