Primary small-cell neuroendocrine carcinoma of the bladder: a very rare histological subtype.

Primary small cell neuroendocrine carcinoma (SCNC) of the bladder is an exceptionally aggressive malignancy. We report the case of an 80-year-old male, a chronic smoker, presenting with an 8-month history of intermittent total hematuria. Cystoscopy revealed a 72 mm mass infiltrating the bladder dome, posterior, and lateral walls. Histopathological analysis of transurethral resection specimens demonstrated a necrotic diffuse proliferation of monomorphic small cells infiltrating the muscularis propria. Immunohistochemistry showed positivity for synaptophysin, chromogranin A, CD56, and TTF1, whereas GATA3 and p63 were negative. The Ki-67 index exceeded 90%. Systemic staging (cT3bN0M0) confirmed the primary bladder origin. Although multimodal management, including neoadjuvant chemotherapy and radical cystoprostatectomy, was recommended, the patient-initiated chemotherapy but declined surgery. Primary bladder SCNC is a highly invasive entity requiring early diagnosis and multidisciplinary care. The diagnosis is strictly anatomopathological. Differentiating this entity from primary pulmonary small cell carcinoma is a critical challenge, making systemic radiological staging mandatory.