Primary carcinoid tumors of the urinary bladder and prostatic urethra: a clinicopathologic study of 6 cases.

Primary carcinoid tumors of the urinary bladder are exceedingly rare. Although they have been considered to be potentially malignant neuroendocrine neoplasms, some previously reported cases were associated with a carcinoma component that might have altered the outcome. Only 8 histologically well-documented cases of pure carcinoid tumors of the bladder and 1 of the prostatic urethra have been reported in the literature. In this study, we describe 6 additional primary pure carcinoid tumors arising in the bladder (5 cases) or prostatic urethra (1 case). Patients (4 male, 2 female) ranged in age from 45 to 60 years (average, 55 y) and presented with hematuria (n = 5 of 6), obstruction (n = 1 of 6), or for concurrent genitourinary disease (n = 1 of 6). All 6 cases shared gross and microscopic findings. Cystoscopic examination showed small, smooth surfaced, or polypoid nodules. The 5 cases in the bladder were all located within or near the trigone and bladder neck region. Microscopically, these 6 tumors were subepithelial and confined within the lamina propria, associated with adjacent cystitis cystica et glandularis. The tumors were composed of uniform, cuboidal, or columnar cells with finely stippled chromatin and inconspicuous nucleoli in a prominent pseudoglandular pattern composed of acinar and cribriform structures. The cells had moderate-to-abundant cytoplasm and basally located Paneth cell-like eosinophilic granules. Although occasional atypical cells with prominent nucleoli could be seen, mitotic activity was absent or rare and cases lacked necrosis. Neuroendocrine differentiation was confirmed by immunohistochemistry in all 6 cases. All tumors were completely excised by biopsies. There was no evidence of disease recurrence or progression in all 6 patients, including 3 patients who had clinical follow-up for >4 years. Primary pure carcinoid tumors of the urinary bladder (and prostatic urethra) have distinct pathologic characteristics, with their prominent pseudoglandular features leading to difficulty in diagnosis. They are likely to have a very favorable clinical outcome, and should be distinguished from mixed carcinoid tumors or urothelial carcinomas with neuroendocrine differentiation that show focal carcinoid-like histologic features.