Neuroendocrine tumors of the urinary bladder

Primary neuroendocrine tumors of the urinary bladder are relatively rare and are comprised of a heterogeneous group of neoplasms. These include well-differentiated neuroendocrine tumors (WDNETs) or carcinoid tumors; poorly differentiated neuroendocrine carcinomas (NEC), including small cell neuroendocrine carcinoma (SCNEC) and large cell neuroendocrine carcinoma (LCNEC); and paraganglioma. These tumors are believed to arise from native neuroendocrine cells in the urothelial lining in the case of WDNETs, transdifferentiation of urothelial carcinoma cells in the case of poorly differentiated NECs, and chromaffin cells in autonomic ganglia in the case of paraganglioma. These tumors have different treatment protocols and clinical outcomes than conventional urothelial carcinoma, with SCNEC and LCNEC having a more aggressive course and worse outcomes and WDNET and paraganglioma having a more indolent course and better outcomes. Therefore, the proper recognition of these tumors is important. The epidemiological data; clinical information; histopathologic, immunohistochemical, and molecular features; prognostic factors; and therapeutic approaches of these entities are discussed in this chapter.