D. Well-differentiated neuroendocrine carcinoma (carcinoid tumor)
Neuroendocrine carcinomas of the lung represent a complex family of tumors that range from well differentiated (carcinoid tumor) to moderately differentiated (atypical carcinoid tumor) to poorly differentiated (small-cell carcinoma and large-cell neuroendocrine carcinoma). Many histological variants have been described for these tumors and their classification still remains controversial. Similar tumors have also been described in the gastrointestinal tract, head and neck area, and genitourinary tract, among others.
Although the histology and immunohistochemistry of these tumors is very similar, when these tumors occur in particular anatomical areas such as lung, the may have other markers that may help in defining their site of origin (ie, TTF-1 in lung tumors and CDX-2 in gastrointestinal tumors).
1. Moran CA, Suster S, Coppola D, Wick MR. Neuroendocrine carcinomas of the lung: a critical analysis. Am J Clin Pathol. 2009;131:206-221. PubMed