Fine needle aspiration cytology of atypical carcinoid of the lung.

The cytologic features of eight atypical carcinoid tumors of the lung, as observed in fine needle aspiration (FNA) specimens, are described in detail. They were compared with 21 pulmonary squamous-cell carcinomas, 16 adenocarcinomas, 5 small-cell undifferentiated carcinomas, 3 large-cell undifferentiated carcinomas and 1 typical carcinoid tumor. Atypical carcinoid tumor was easily distinguished from the other pulmonary neoplasms in most instances. Only two poorly differentiated squamous-cell carcinomas (one of which had atypical carcinoid as a component) and one small-cell undifferentiated carcinoma had similar cytologic features. One atypical carcinoid also had cytologic features similar to small-cell undifferentiated carcinoma. Because atypical carcinoid and small-cell undifferentiated carcinoma, at times, may be difficult to separate in FNA specimens, surgical resection of all stage I neoplasms with cytologic features evocative of either neoplasm is recommended.