[Follicular dendritic cell sarcoma: a clinicopathologic study of 8 cases]

To investigate clinicopathologic features, immunophenotypes and differential diagnoses of follicular dendritic cell sarcoma/tumor (FDCS).

Eight cases of FDCS were studied using histological and immunohistochemical examinations and EBER in situ hybridization, with a review of the related literatures.

There were 5 male and 3 female patients with a median age of 50 years. The sites of involvement included lymph node (4 cases), tonsil, nasopharynx, liver, and spleen (1 case each, respectively). The predominant microscopic features histologically included storiform, fascicular, diffuse, whorled and nodular in patterns. The neoplastic cells, dispersed by the infiltrated small lymphocytes, were characterized by abundant eosinophilic or fine granular cytoplasm with indistinct cell borders, and syncytial in appearance. The nuclei of the tumors were ovoid, round to spindled in shape with vesicular or stippled chromatin and small distinct nucleoli. Mitotic figures varied among cases. Pseudovascular spaces and perivascular cuffing were observed in some cases. One case of FDCS involving lesion in liver showed a background of abundant lymphocytes mixing with dispersed spindle or ovoid neoplastic cells having delicate chromatin, mild nuclear atypia, irregular/vesicular nuclei and distinct nucleoli. The neoplastic cells were positive for CD21, CD35, clusterin, and weakly positive for CD68, EMA, S-100 and EGFR. Ki-67 stain showed a variable expression among cases. EBER was positive in 2 cases.

FDCS is a rare malignant tumor with a tendency to relapse and metastasis. Combined morphological and immunophenotypical analysis is necessary to reach a correct diagnosis.