Malignant fluids from metastatic colorectal carcinomas characteristically contain clusters of obviously malignant cells, and the presence of some cells demonstrating a palisading and/or columnar appearance provides a clue to the diagnosis.
Small cell carcinoma cells appear as small malignant cells that may be round to spindle shaped. Cytoplasm is scanty or absent and nuclear chromatin is coarse. Nucleoli may be more evident in fluids than in bronchial specimens. The malignant cells may be single or in small clusters, and nuclear molding is characteristic. Single file arrangements may also be present.
This low power appearance of “cannonballs” of malignant cells is one of the characteristic patterns of metastatic breast carcinoma in fluids.
Malignant lymphoma cells appear singly and nuclear membrane irregularities may be prominent. N/C ratios are often high, with scanty cytoplasm; however, large cell lymphoma cells may display more abundant cytoplasm. Massive karyorrhexis in a fluid displaying a single cell pattern of neoplastic cells is highly suggestive of lymphoma. On DiffQuik staining, lymphoglandular bodies, which are small blue fragments of the cytoplasm of lymphoid cells, may be evident. Immunocytochemistry and flow cytometry may be helpful in establishing a specific diagnosis.
Mesothelioma often produces very large groups containing many neoplastic cells. The borders of the cell clusters are often irregular or “knobby,” in contrast to many carcinomatous cell clusters. In addition, single neoplastic cells are present and display a spectrum of cytologic atypia, with cells ranging from benign-appearing mesothelial cells to malignant cells, many of which retain mesothelial features.