a Cytologic features of metastatic pulmonary adenocarcinoma in pleural effusions. Clusters of cells showing a solid (3-dimensional clusters of cells with dense cytoplasm pleomorphic nuclei) and micropapillary-like architecture (tight small clusters of cells with predominantly eccentric nuclei). ×60. Pap, cytospin. b Clusters of cells showing solid (i.e., nests of cells with well-defined cytoplasmic membranes; some of the cells have a dense cytoplasm and others show a clear cell change) with a micropapillary-like architecture. ×60. Hematoxylin and eosin, cell block. c Immunohistochemical stain showing 3-dimensional clusters of cells (solid-like architecture) positive for TTF-1. ×40.