Electron microscopic identification of the colorectal origins of tumor cells in pleural fluid.

Cellular material from metastatic rectal and lung adenocarcinomas was recovered from pleural and pericardial fluids, respectively. It was examined by electron microscopy (EM) to determine if certain ultrastructural features, which are primarily prominent in colorectal adenocarcinomas, were maintained in the tumor cells in metastatic fluid. These features include the presence of microvilli with dense microfilamentous cores that extend deeply into the apical cytoplasm (cytoplasmic rootlets) and an abundance of glycocalyceal bodies. It was found that tumor cells from the patient with a primary rectal adenocarcinoma exhibited these critical distinguishing characteristics. The cells from the lung adenocarcinoma, while containing many well-developed microvilli, did not possess cytoplasmic rootlets or glycocalyceal bodies. In addition, and possibly of more diagnostic significance, is the observation that the presence of microvilli and cytoplasmic rootlets remained evident in tissue pieces and cell blocks initially processed in paraffin and then reembedded for EM.