[Clinicopathological Features of Follicular Dendritic Cell Sarcoma].

Objective To explore the clinicopathological and immunohistochemical characteristics of follicular dendritic cell sarcoma(FDCS)and the expressions of IgG and IgG4. Methods We retrospectively analyzed the clinicopathological and immunohistochemical data of 9 pathologically confirmed FDCS cases in Peking Union Medical College Hospital from January 2005 to December 2018.Immunohistochemical staining of IgG and IgG4 were performed,and Epstein-Barr virus(EBV)-encoded RNA(EBER)in situ hybridization were carried out. Results Nine cases of FDCS included 4 men and 5 women aged 16-53 years [mean(38.2±9.7)years].The clinical manifestations included masses,lymph node enlargement,rash,and fever.The tumors were located in lymph node,retroperitoneal region,adrenal gland,neck,axillary region,and liver,respectively.Ultrasound showed clear boundary cystic or solid mass with maximum diameters of 1.5-15.0 cm.Microscopically,the spindle tumor cells were arranged in solid and storiform patterns with abundant and slightly stained cytoplasm,vacuolated nuclei,and small nucleoli.The mitosis was 1-3/10 high power fields,and necrosis was found in 5 cases.Immunohistochemically,the tumor cells were positive for CD21(6/9),CD35(6/9),and CD23(7/9). Conclusions FDCS is a rare malignant tumor,which is easy to be missed.The combination of CD21,CD35,and CD23 is helpful for diagnosis.Hyaline-vascular type Castleman's disease may be the precursor of FDCS,and there may be only a small number of IgG4-positive plasma cells in FDCS.Surgical resection remains the main treatment for FDCS.