A 65-year-old man presented with a sensation of an abdominal mass and a presentation of an incomplete bowel obstruction. He had a previous history of hypertension and hyperlipidemia; percutaneous internal coronary stenting was performed 9 years ago, and he is currently taking betaloc 47.5 mg, aspirin 100 mg, and rosuvastatin 10 mg, without a remarkable family history. Physical examination showed that his vital signs were within normal range. An abdominal examination could reach a massive mass extending from the middle abdomen to the pelvic cavity, which is about 16 cm in size, poor in mobility, and tough in texture; the rest abdomen was soft and non-tender, without signs of peritoneal irritation. Initial lab tests including complete blood count and tumor markers presented in the. Contrast-enhanced CT of the abdomen showed that a large, mass-confounding density was occupied in the omentum majus area of the middle and lower abdominal wall (). A 3D reconstruction of the images was performed (). To clarify the relationship between tumor and colon, colonoscopy was performed (). The preoperative diagnosis of the patient was intestinal obstruction and abdominal tumor, and he underwent surgery in May this year. During the operation, we observed that the tumor originated from the omentum majus and invaded the middle segment of the transverse colon, the anterior wall of bladder, and the abdominal wall. No other distant metastasis was found. The patient underwent surgical treatment that included a 5-cm transverse colon at each end with the mass involvement, the involved bladder tissue, and the lower umbilical range of about 10 * 10 cm of the adhesion peritoneum and rectus abdominal sheath. The complete tumor was removed and elevated colostomy was performed. () The operation time of the patient was 282 minutes, the intraoperative bleeding was 100 ml, and there was no postoperative complication. Postoperatively, the patient was generally in a stable condition and discharged 9 days later. The size of the tumor was 18 * 12 * 6 cm. The cut surface of the tumor was gray, with hemorrhage in the center. Histologically, the neoplasm was lobulated and consisted of small round cells with amphiphilic cytoplasm and round to ovoid mononuclear hyperchromatic nuclei. There was marked mitosis and necrosis. The neoplasm involved the surrounding adipose tissue and was infiltrated into the intestinal and bladder wall. () Immunohistochemistry showed that the tumor cells differentiated into epithelium, muscle, and nerve. Tumor cells expressed an epithelial marker, such as CK(pan), CAM5.2, and EMA. Desmin, NSE, vimentin, and CD99 proteins were strongly expressed in the tumor cells. The positive rate of Ki-67 was about 60%. Some tumor cells expressed MC(HBME1). However, GATA-3, P63, CK5/6, Syn, CgA, CEA, Wilms tumor, MyoD1, myogenin, NKX2.2, calretinin, CD56, S-100, SOX-10, and PGP9.5 were negative. Fluorescence in situ hybridization (FISH) revealed EWSR1-WT1 gene rearrangement at 22q12, confirming the diagnosis of a desmoplastic small round cell tumor (). In August, the patient was reexamined with abdominal enhanced CT and chest CT, and was found with no tumor recurrence and metastasis. The patient has received chemotherapy four times since the operation. The chemotherapy regimen was oral dacarbazine 0.5 g d1–d4 and intravenous doxorubicin hydrochloride liposome 50 mg d1.