OBJECTIVETo study the clinicopathologic features of follicular dendritic cell sarcoma (FDCS) and its differential diagnosis.

METHODSTen cases of FDCS were studied by light microscopy, immunohistochemistry and in-situ hybridization. The clinical features and follow-up information were analyzed.

RESULTSAmongst the 10 cases of FDCS studied, the male-to-female ratio was 1:1. The mean age of the patients was 42 years. Six of them were located in cervical and peritoneal lymph nodes and four in extranodal sites (including tonsil, pelvic cavity, tail of pancreas and spleen). Histologically, the tumor cells had whorled, storiform or diffuse growth patterns. They were spindle in shape and contained syncytial eosinophilic cytoplasm, with round or oval nuclei, vesicular chromatin, distinct nucleoli and a variable number of mitotic figures. Multinucleated tumor giant cells and intranuclear pseudoinclusions were occasionally seen. There was a sprinkling of small lymphocytes and neutrophils within the tumor as well as in the perivascular region. Immunohistochemical study showed that the tumor cells were diffusely or focally positive for CD21, CD23, CD35 and D2-40, but negative for LCA, CD20, CD3, CD1a, HMB45 and CK. Some of them showed EMA, CD68 and S-100 reactivity. In-situ hybridization for Epstein-Barr virus-encoded RNA (EBER) showed positive signals in only one case (which was diagnosed as inflammatory pseudotumor-like FDCS). Of the 7 patients with follow-up information available (duration: 2 months to 39 months; mean: 14 months), 2 cases with paraneoplastic pemphigus died of pulmonary infection at 5 and 7 months respectively. The remaining 5 patients were alive and disease-free after surgical excision (+/- chemotherapy and radiotherapy).

CONCLUSIONSFDCS is a rare low to intermediate-grade malignant tumor. Appropriate application of FDC markers, such as CD21, CD35 and D2-40, would be helpful for arriving at a correct diagnosis. Most cases are associated with good prognosis after surgical treatment, with or without chemotherapy and radiotherapy. Patients with paraneoplastic pemphigus carry a less favorable prognosis.