Interwoven Dendritic Processes of Follicular Dendritic Cell Sarcoma Demonstrated on Ultrafast Papanicolaou–Stained Smears

Background Follicular dendritic cell (FDC) tumor is a rare tumor derived from accessory cells in the lympboid follicles. FDC tumors are typically diagnosed on histology based on-immunoreactivity to at least I of the FDC markers (CD21, CD23 or CD35) or based on the characteristic ultrastructural feature of long, interwoven, cytoplasmic, dendritic processes connected by desmosomes. Case We observed novel cytologic features of FDC sarcoma in a liver fine needle aspirate of a 46-year-old man status post surgery and chemotherapy for FDC sarcoma, originating in the gastrointestinal tract with metastases to the liver, pancreas and spleen. In the Diff-Quik- and Papanicolaou-stained smears, the tumor cells presented in syncytial fragments as well as single cells, as previously reported in the cytologic literature. However, the single cells were interconnected to neighboring single cells via long, thin, threadlike cytoplasmic processes in ultrafast Papanicolaou (UFP)-stained smears. The tumor cells possessed multipolar cytoplasmic processes rather than unipolar ones, as previously reported. Conclusion The ultrastructural features of a web of interwoven, dendritic, cytoplasmic processes of FDC tumor was demonstrated for the first time on cytology. Observation of this feature may allow the diagnosis to be made on cytology prior to histology, immunohistochemistry or electron microscopy.