[Follicular dendritic cell sarcoma: a clinicopathologic study of five cases].

Objective: To study the clinical pathological features and immunophenotype of follicular dendritic cell sarcoma (FDCS) with discussion on its diagnostic clues to improve diagnostic level.

Methods: Five cases of FDCS were analyzed by clinical, pathologic and immunohistochemistry methods.

Results: Five cases of FDCS were located in the cervical lymph node. Microscopically, the normal architectures were effaced by ovoid, spindle-shaped with fascicular, diffuse or whorled patterns and with rich lightly eosinophilic cytoplasm, syncytial appearance. Nuclei tend to show irregular clustering, scattered multinucleated giant cell. Nucleoli often distinct, sometimes prominent. Mitotic count variable, may show significant cellular pleomorphism. Immunohistochemical studies show that the tumor cells were positive for CD21, CD35, but negative for CD1a, CD34, CK and HMB45. Under electron microscopy, the tumor cells possessed long villus cytoplasmic processes and desmosome-like junctions, Birbeck granules were absent.

Conclusions: FDCS is a rare malignant tumor and differential diagnosis includes Langerhans cell sarcoma, interdigitating dentric cell sarcoma, malignant fibrous histocytoma, melanoma, metastatic spindle cell carcinoma and others. Immunohistochemistry and electron microscopy are necessary for a correct diagnosis.