Female, 52 years old, was admitted to hospital on 24 July 2018 due to "abdominal distension for more than 2 months". The patient developed postprandial abdominal distension with gradual weight gain 2 months before admission. In the local hospital, the abdominal CT scan showed a huge mass in the abdominal cavity with clear boundaries, except for huge leiomyosarcoma. Past history: Uterine fibroids were discovered 2 months ago, with no history of chronic disease, infectious disease, allergy and trauma. Family history: Brother suffers from lung cancer. Physical examination after admission: general condition acceptable, height 163 cm, weight 65.5 kg; The middle and upper abdomen were swollen, with palpable ductile masses, about 10 cm ×8 cm in size, with clear boundaries, no tenderness, no obvious sensation of mobility, unsatisfactory palpation of liver, gallbladder, pancreas and spleen, and bowel sounds 3 times/min. Laboratory test: Hemoglobin 102 g/L, no abnormalities in other test results. The enhanced CT scan showed that the size of the tumor was about 14.6 cm ×9.4 cm, with uneven enhancement and no obvious enlargement of the peripheral lymph nodes. It is recommended to consider the possibility of gastrointestinal stromal tumor (GIST) of gastric origin first (Figure 1）。 Electronic gastroscopy showed chronic atrophic gastritis with multiple polyps in the lower 2/3 of the gastric cavity, and biopsy pathology showed chronic inflammation of the gastric mucosa with low-grade intraepithelial neoplasia. Endoscopic ultrasound revealed a huge hypoechoic mass immediately adjacent to the stomach wall. The local ultrasound section size was about 13.3 cm ×9.2 cm, and the internal echo of the lesion was uneven, considering interstitial mass; Because the lesion is too large, the relationship between the position and the surrounding organs is not good; The stomach wall was collected at the lesion, and the relationship with the stomach wall showed poor (Figure 2）。 Three endoscopic ultrasound-guided fine-needle aspiration (EUS-FNA) were performed to clarify the histological origin of the tumor, and only a very small number of degenerative abnormal cells were found (Figure 3）。 After multi-disciplinary comprehensive discussion, PET-CT was performed to distinguish GIST from other types of mesenchymal tumors, and the results showed that the tumor may originate from peritoneal mesenchymal tissue. The 2nd multidisciplinary comprehensive discussion evaluated the possibility of radical resection of the tumor and performed gastric wedge resection on the patient on August 9, 2018. Intraoperatively, it was found that the tumor was located in the left middle and upper abdomen, with an intact capsule, and originated from the large curved side of the anterior wall of the gastric fundus (Figure 4), which is connected to the stomach wall by a pedicle, and the pedicle part is about 2 cm wide (Figure 5）。 No peripheral lymph node metastasis, abdominal or pelvic metastasis or peritoneal dissemination were found during intraoperative exploration, and wedge gastrectomy was performed. The postoperative pathological examination results showed that a tumor was found under the gastric mucosa of the submitted sample, about 20 cm ×17 cm ×13 cm in size, with a gray-white gray-yellow section, which belonged to a spindle cell tumor; Immunohistochemical staining results showed that smooth muscle actin (+), desmin (+), CD34 (partial +), CD117 (-), S-100 (-), Dog-1 (-), Ki-67 (hot zone 10% +) (Figure 6）； The final diagnosis was gastric leiomyoma. The patient was discharged 4 d postoperatively, and no recurrence was observed at 1 year postoperative follow-up.
