Small cell carcinoma of the bladder is an uncommon and rather aggressive
bladder tumor, representing less than 1% of all vesical
tumors.
Small cell carcinoma of different organs has been shown to express markers of neuroendocrine differentiation, and also
thyroid transcription factor 1 (TTF-1). TTF-1 is a
transcription factor and its expression has been shown mainly in pulmonary
small cell carcinomas and
adenocarcinomas and in thyroid
tumors. Although it was initially proposed as a useful marker to delineate the origin of metastatic
adenocarcinomas from the lung, its expression is being increasingly reported in
tumors from different origins. The goal of this review is to analyse the immunohistochemical profile of
small cell carcinoma of the bladder and to compare it to classical urothelial cell
carcinomas. With this aim we have reviewed the small cell bladder
carcinomas diagnosed in a single tertiary hospital in Madrid (Fundación Jiménez Díaz) in the last 12 years. We have found 6 pure
small cell carcinomas and performed a wide panel of immunohistochemistry, including cytokeratins 7 and 20,
enolase,
chromogranin,
synaptophysin, CD56 and TTF-1 to these
tumors and also to 30 high grade urothelial cell
carcinomas of usual type. Only one of our
small cell carcinoma cases showed positivity for TTF-1, while five expressed CD56 and four
neuron-specific enolase. None of our cases expressed
cytokeratin 20 or 7. To our surprise we found a case of conventional urothelial cell
carcinoma expressing focally TTF-1. These results are in accordance with the current literature, although our rate of TTF-1 expression (16.6%) is on the low end of the spectrum.