The Expression of TTF-1 in Small Cell Carcinoma of Urinary Bladder

Abstract

Small cell carcinoma (SMCC) of the urinary bladder is a rare tumor, accounting for less than 1% of all malignant neoplasms in the urinary bladder. Recently, thyroid transcription factor-1 (TTF-1), a putative marker for tumors originating from the lung and thyroid, was found to be expressed in SMCC of the urinary bladder, albeit in only a very small number of cases. Herein we report two additional cases of SMCC of the urinary bladder expressing TTF-1. The first patient was a 68-year-old white male with a 5-year history of a small focus of prostatic adenocarcinoma (biopsy proven) who was being treated with brachytherapy. He subsequently developed multiple large nodules at the base of the bladder, which by biopsy identified the presence of loosely cohesive small cells with minimal cytoplasm, coarsely and finely granular chromatin and indistinct nucleoli. Tumor cells were positive for TTF-1, CD56, chromogranin, synaptophysin and Cam 5.2, and negative for PSA. The location, morphological and immunochemical features of the tumor were diagnostic for SMCC of the urinary bladder. The second patient was a 76-year-old white female with a history of recurrent episodes of urinary tract infections. A biopsy showed a poorly differentiated carcinoma. The subsequent cystectomy revealed the presence of a 4.5 x 4.5 x 2.1 cm. tumor composed of a mixture of infiltrating high grade urothelial carcinoma and small cell carcinoma. The small cell component possessed similar morphological and immunohistochemical features as previously described in the first case, including positive expression for TTF-1. These two cases illustrate and concur with previous assertions that TTF-1 cannot be used to distinguish primary SMCC of the urinary bladder from metastatic SMCC of lung. [N A J Med Sci. 2009;2(3):94-96.]