A rare case of inflammatory myofibroblast tumor of the stomach successfully treated by inverted laparoscopic and endoscopic cooperative surgery

BACKGROUND: An Inflammatory myofibroblastic tumor (IMT) is a rare intermediate malignancy characterized by myofibroblast proliferation and inflammatory cell infiltration. Various organs are the primary sites of origin. However, primary tumors originating in the stomach tend to be extremely rare, making the diagnosis difficult. Herein, we present a case of IMT originating in the stomach that was effectively managed using inverted laparoscopic endoscopic cooperative surgery (LECS). CASE PRESENTATION: A 47-year-old male who was admitted to the hospital because of a submucosal tumor that was discovered during upper gastrointestinal endoscopy. The diameter of the tumor was approximately 20 mm. A KIT-negative gastrointestinal stromal tumor was suspected based on the biopsy findings. Therefore, partial resection of the stomach was performed using inverted laparoscopic and endoscopic cooperative surgery. Histopathological examination revealed collagen fiber proliferation from the submucosal layer to the muscular layer, accompanied by infiltration of spindle-shaped cells, lymphocytes, and numerous inflammatory cells. Immunohistochemistry results were positive for SMA and negative for CD34, desmin, and c-kit. IgG4-positive cells were observed with an IgG4/IgG ratio > 50%, and specific nuclei were positive for ALK. Therefore, IMT was diagnosed. This condition may be difficult to diagnose both before and after surgery because of its rarity and submucosal tumor-like morphology. CONCLUSION: When a submucosal tumor originating in the stomach is observed, IMT should be considered. Partial resection of the stomach with LECS and immunohistochemical diagnosis may be useful.