Achieving Stable Disease in an Adult with Malignant Gastrointestinal Tumor following Cabozantinib Treatment: Case...

Malignant gastrointestinal neuroectodermal tumor (GNET) is a rare and aggressive neoplasm that is characterized by EWSR1 rearrangements. Most patients present with metastatic disease. There are no established treatment guidelines, and systemic therapy options remain poorly defined.

A woman in her late 30s presented initially with right upper quadrant pain and bloating. Endoscopic biopsy of a duodenal mass revealed a SOX10-positive malignant neoplasm. Molecular testing identified an EWSR1:CREB1 fusion, confirming GNET. Initial treatment with ipilimumab and nivolumab resulted in disease progression. Subsequent therapies included a selective interleukin-2 agonist clinical trial, nivolumab/relatlimab, and temozolomide, all associated with continued progression. Cabozantinib was initiated after further radiographic progression. Follow-up imaging demonstrated tumor regression, and the patient maintained stable disease for 15 months before mild progression.

Metastatic GNET has a poor prognosis and lacks standardized systemic therapy. This case demonstrates durable disease stabilization with cabozantinib after progression on immunotherapy and chemotherapy. Tyrosine kinase inhibition may represent a promising therapeutic strategy in GNET and warrants further investigation.