Enteric-type urachal adenocarcinoma harboring an EIF3E::RSPO2 fusion with durable response to immune checkpoint inhibition: a case report

Urachal carcinoma (UrC) is a rare malignancy accounting for <1% of bladder cancers, most commonly presenting as adenocarcinoma with enteric differentiation. Systemic treatment for advanced disease is not standardized. Increasing evidence indicates that UrC shares molecular features with colorectal cancer, supporting genomic profiling to identify actionable alterations. We report a case of enteric-type urachal adenocarcinoma in an adult patient with metastatic progression. Next-generation sequencing revealed an EIF3E::RSPO2 fusion, a rare genomic rearrangement recently documented in isolated cases of UrC and implicated in Wnt pathway activation. The patient on treatment with atezolizumab demonstrated an excellent clinical and radiological response with a remarkably long progression-free survival of >6 years. This case highlights the heterogeneity of UrC, the clinical value of molecular characterization, and the potential for immunotherapy to provide meaningful benefit in select patients. Ongoing real-world reporting is critical to inform treatment strategies for this rare tumor.