Immunohistochemical profile of urothelial and small cell carcinomas of the bladder.

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.