A case report of malignant neuroectodermal tumor of the gastrointestinal tract without common gene fusion in a soft tissue tumor.

Background: Malignant gastrointestinal neuroectodermal tumor (GNET) is extremely rare in soft tissue sarcoma and occurs mainly in the small intestine of young adults, without sex predilection. Local recurrence and metastasis are common in GNET, resulting in a poor prognosis. GNETs are histologically and immunohistochemically similar to many sarcomas, especially clear cell sarcoma (CCS), making their identification difficult. The majority of GNET cases have EWSR1 gene rearrangements, which can be characterized at the genetic level and provide important clues for diagnosis of GNETs. However, very few studies have been conducted on GNET cases without common gene fusion in soft tissue tumors. Case Description: A 48-year-old woman was admitted due to melena and worsening fatigue and dizziness. An abdominal computed tomography scan revealed a mass arising from the stomach with hepatic metastases. Based on the evidence of histology and immunohistochemistry, the final diagnosis was GNET. Then we performed a gene analysis of the tumor using fluorescence in situ hybridization and next-generation sequencing, including whole-exome sequencing and multiplex polymerase chain reaction. We did not detect any common gene fusion in the soft tissue tumors, such as EWSR1. The results of the whole-exome sequencing revealed 11 genes involved in the occurrence and development of soft tissue sarcomas. Six months after surgery, the patient's abdominal computed tomography (CT) showed new metastases in the liver. Hence, we used targeted therapy and immunotherapy to treat her and liver metastases were reduced. Conclusions: Genetic diagnosis is one of the important evidences for the diagnosis of GNET. However, the cases of GNET with negative EWSR1 expression are rare, which makes clinical diagnosis difficult. Our findings may extend genetic understandings of GNET and provide more help for clinical diagnosis of GNET. 2022 Journal of Gastrointestinal Oncology. All rights reserved.