Primary small cell neuroendocrine carcinoma of the urinary bladder: a clinicopathologic, immunohistochemical, and ultrastructural evaluation.

Small cell neuroendocrine carcinoma (SCNEC) of the urinary bladder is a rare but aggressive neoplasm that usually exhibits neuroendocrine differentiation. Here, the authors report a case of SCNEC in an 80-year-old man. The patient had gross hematuria and nodular mass involving the wall of the urinary bladder. Total cystectomy was done. The tumor consisted of small, uniform, round, and spindled-shaped cells with chromatin dark nuclei and numerous mitotic figures. The cells were reactive for chromogranin, neuron-specific enolase (diffuse), and keratin (focal). Ultrastructural studies revealed neurosecretory granules and intermediate filaments. The diagnosis of SCNEC with focal high-grade urothelial component was established. No metastasis was found at the time of diagnosis and the patient refused further chemotherapy or radiotherapy. The histogenesis, differential diagnosis, and prognosis of SCNEC of the urinary bladder were discussed.