Primary carcinoid tumor of the bladder arising beneath an inverted papilloma

We describe a 54-year-old woman with a primary carcinoid tumor of the bladder arising beneath an inverted papilloma diagnosed by light microscopy and immunohistochemical studies. After the patient complained of hematuria and voiding difficulties, a polypoid mass was detected during cystoscopy and removed for examination. The distinctive histologic features of an inverted papilloma were readily identified. The characteristic pattern of a carcinoid tumor was confirmed with immunohistochemical studies.