Cytomorphology and marker expression of malignant neuroendocrine cells in pleural effusions.

Three cases of pulmonary neuroendocrine carcinoma with malignant pleural effusions were retrospectively studied to determine if cellular morphology and expression of neuroendocrine markers were the same in the fluid as in the solid milieu. In fluids, changes were noted in cell grouping, shape and cytoplasm. Neuroendocrine markers expressed in both solid and dispersed tumors were neuron-specific enolase (NSE) in all cases and leu-enkephalin in one case. Vasoactive intestinal polypeptide (two cases) and serotonin (one case) were detected only in the solid tumor. ACTH, bombesin and calcitonin were not expressed. We tentatively conclude that, in effusions, neoplastic neuroendocrine cells may alter their cytostructure, growth patterns and marker expression capabilities. NSE appears to be the most reliable neuroendocrine marker for use in small samples and with varying preparatory methods.