Case Report: Clinicopathological features of bladder neuroendocrine neoplasm: a retrospective case series of nine cases and literature review.

Primary bladder neuroendocrine neoplasm (BNEN) is an uncommon but clinically aggressive malignancy, and evidence guiding its diagnosis and management remains limited. This retrospective study analyzed nine patients diagnosed with BNEN at a single institution between 2014 and 2024, with pathological classification confirmed by morphology and neuroendocrine immunohistochemical markers. Clinical features, histological subtypes, treatment strategies, and follow-up outcomes were reviewed. Most patients presented with painless gross hematuria and advanced-stage disease. Histologically, the cohort showed marked heterogeneity, including small cell neuroendocrine carcinoma (SCNEC), large cell neuroendocrine carcinoma (LCNEC), paraganglioma (PGL), and mixed neuroendocrine neoplasms. All cases expressed CD56 and synaptophysin, while Ki-67 indices indicated high proliferative activity in most tumors. Despite multimodal treatment, prognosis remained poor. Findings related to immunotherapy were preliminary and should be interpreted with caution. These findings highlight the aggressive and heterogeneous nature of BNEN and support individualized multimodal management, with further studies needed to clarify the role of immunotherapy.