* CD56 Positive
* Napsin A Negative
====Resident Questions====
* <spoiler text="What is the explanation for the occasional prominent nucleoli and what is the differential diagnosis?">The differential diagnosis includes large cell neuroendocrine carcinoma, and possibly nonkeratinizing squamous cell carcinoma and adenocarcinoma. In this case, we know that we are dealing with a poorly differentiated neuroendocrine carcinoma based on immunohistochemistry. In addition, except for the occasional nucleoli, this lesion has all of the features of a small cell carcinoma (scant cytoplasm, nuclear molding). In this case, the possibility of a poorly differentiated carcinoma with mixed large cell and small cell features may not be able to be completely ruled out on cytology of the pleural fluid. It has been determined that prominent nucleoli may be seen in small cell carcinomas up to 24% of the time (Khalbuss WE The cytomorphologic spectrum of small-cell carcinoma and large-cell neuroendocrine carcinoma in body cavity effusions: A study of 68 cases. CytoJournal 2011, 8:18. [[http://www.cytojournal.com/article.asp?issn=1742-6413;year=2011;volume=8;issue=1;spage=18;epage=18;aulast=Khalbuss]]
</spoiler>
