A review of cytologic findings in neuroendocrine carcinomas including carcinoid tumors with histologic correlation

BACKGROUND, The nosology of neuroendocrine neoplasia has evolved substantia lly in recent years. The aim of this study was to review the authors' insti tutional experience and diagnostic accuracy for cytologic specimens of neur oendocrine carcinoma (NEC) and to identify features most suggestive of neur oendocrine differentiation. METHODS. The cytologic and histologic findings of 29 archival NEC in which cytology preceded biopsy or resection were compared. The study was comprise d of 6 carcinoid tumors, 3 atypical carcinoid tumors, 17 high grade NEC (5 small cell, 9 large cell, and 3 mixed small/large cell), and 3 combined NEC /nonneuroendocrine carcinomas. Cytologic material was derived from 21 fine- needle aspirates (FNA), 6 bronchial brushing/washings, and 2 gastrointestin al tract brushings. RESULTS. Of the 29 cases, the correct cytologic diagnosis was rendered in 1 1. Two cases were identified as NEC but were graded incorrectly. The remain ing 16 cases were interpreted as nonsmall cell carcinoma (8 cases); diagnos tic or suspicious of carcinoma, not otherwise specified (7 cases); and atyp ical, indeterminate for malignancy (1 case). On review, neuroendocrine feat ures were identified in 14 of the latter 16 cases. CONCLUSIONS. The cytologic diagnosis of NEC, both high and low grade, can b e difficult. Because of acinus-like formations and columnar cell shapes, lo w grade NEC may be mistaken for adenocarcinoma. Small cell carcinomas, espe cially in bronchial brush and wash preparations, may be difficult to classi fy beyond malignant. Large cell NEC may be confused with nonneuroendocrine carcinomas because of abundant cytoplasm and nucleoli. Attention to the pre sence of loose cell aggregates in a background of singly dispersed cells; f eathery patterns created by tumor cells clinging to capillaries; rosette fo rmations; delicate, granular cytoplasm; inconspicuous nucleoli; molding in high grade tumors; and, most important, speckled or dusty chromatin pattern s are useful in identifying neuroendocrine differentiation in cytologic spe cimens. (C) 2000 Amerian Cancer Society.