Clinicopathological features of inflammatory pseudotumour‐like follicular dendritic cell tumour of the abdomen

Inflammatory pseudotumour-like follicular dendritic cell (FDC) tumour is an extremely rare neoplasm. Herein, we report 10 cases of inflammatory pseudotumour-like FDC tumours in the abdomen and analyse their clinicopathological features.Seven patients were male, and three patients were female. The patients' age ranged from 28 years to 68 years (mean age, 52.9 years; median age, 51.5 years). Grossly, the tumour was usually solitary, well circumscribed, and solid, ranging from 23 mm to 233 mm in greatest diameter. Microscopically, the tumour was composed of variable amounts of spindle tumour cells with intense lymphoplasmacytic infiltrate. Unusual morphological findings, including eosinophils focally aggregated in one tumour admixed with multinucleated histiocytes in small clusters, fibrinoid deposits in the walls of ectatic blood vessel with occasional perivascular cuffs of lymphocytes, hyalinized fibrosis, and epithelioid granuloma, were identified. The tumour cells were immunoreactive for CD21, CD23, CD35, smooth muscle actin, and Epstein-Barr virus (EBV)-encoded latent membrane protein 1 (7/10, 70%). EBV-encoded small RNA was positive in all cases by in situ hybridization. The recurrence rate was 10% with a median follow-up of 19 months.Inflammatory pseudotumour-like FDC tumour should be differentiated from inflammatory myofibroblastic tumour, Hodgkin lymphoma, interdigitating dendritic cell sarcoma, and gastrointestinal stromal tumour.