The Role of Targeted Therapy and Immunotherapy in Metastatic GNET/Clear Cell Sarcoma (CCS) of the Gastrointestinal Tract: A Case Report.

Background: Gastrointestinal neuroectodermal tumour (GNET), also known as clear cell sarcoma (CCS) of the gastrointestinal tract, is a rare neural crest-derived malignancy characterized by EWSR1-ATF1 or EWSR1-CREB1 fusions. Due to its rarity, there is limited evidence and no established guidelines for standard management. GNET is aggressive, with high rates of local recurrence, metastasis, and mortality. Case Presentation: We report the case of a 46-year-old woman with a family history of gastrointestinal cancers who was diagnosed in 2020 with an intestinal GNET. She underwent a segmental enterectomy as the first step of multimodal therapy. After three years of follow-up, she developed hepatic and peritoneal metastases. In November 2023, she began combined therapy with the anti-VEGF tyrosine kinase inhibitor cabozantinib and the immune checkpoint inhibitor nivolumab. The patient has maintained stable disease for 18 months with good tolerance and no adverse events. Molecular analysis of the tumour, which showed an EWSR1-CREB1 fusion, supported the selection of targeted therapy and immunotherapy as the preferred treatment approach. Conclusions: Immunotherapy and targeted therapy show promise for GNET/CCS treatment, but clinical standards are lacking, and evidence comes primarily from case reports. Additional data are needed to determine the best sequence and combination of therapies for this very rare disease.