Unusual coexistence: A case of mixed small and large cell neuroendocrine tumor in a bladder previously affected by bilharzial cystitis

Key Clinical Message Neuroendocrine tumors of the bladder are rare, accounting for less than 1% of all bladder tumors. Among these, large cell neuroendocrine carcinoma is an extremely uncommon subtype. We report on a histologically confirmed case of mixed both large and small cells neuroendocrine tumor of the bladder in a 64‐year‐old male with a history of bilharzial cystitis. The diagnosis was made after radical cystectomy with Immunohistochemical staining revealing positivity for synaptophysin, CD56, and AE1/3. While bilharzia is commonly linked to squamous cell carcinoma in the bladder, the potential relationship with neuroendocrine tumors is still relatively unexplored in this context. This case marks the first reported instance of the atypical coexistence of bilharzial cystitis and mixed large and small cell neuroendocrine carcinoma of the bladder. This unique case of coexisting highlights a rare phenomenon warranting further study. Similar associations have been documented in other organs, emphasizing the importance of exploring underlying mechanisms and clinical implications for improved patient care and outcomes.