Inflammatory pseudotumor-like follicular dendritic cell tumor - A distinctive low-grade malignant intra-abdominal neoplasm with consistent Epstein-Barr virus association

Follicular dendritic cell (FDC) tumors are uncommon neoplasms that can invo lve lymph nodes or extranodal sites. They can exhibit a broad spectrum of h istologic appearances and behavior, but the intra-abdominal ones usually pu rsue an aggressive course. The purpose of this study was to characterize a distinctive variant of FDC tumor morphologically mimicking inflammatory pse udotumor through analysis of the clinicopathologic features of 11 cases. Th e patients included 10 women and one man (age range, 19-61 years; median ag e, 40 years) who presented with abdominal discomfort or pain. Six patients had systemic symptoms such as marked weight loss, fever, or malaise. All tu mors occurred in intra-abdominal sites: liver (n = 7), spleen (n = 3), and peripancreatic region (n = I). of the nine patients with follow-up data, si x were alive and well, one developed recurrence at 9 years, and two had rep eated recurrences over many years. Grossly, the tumors were usually solitar y and fleshy, punctuated by areas of hemorrhage and necrosis. Histologicall y, in a background of abundant lymphocytes and plasma cells were dispersed spindle or ovoid cells with vesicular nuclei and distinct nucleoli. The deg ree of nuclear atypia was variable, and some nuclei could be grotesque or r esemble Reed-Sternberg cells. Focally, spindle cell fascicles could be form ed. The atypical cells were immunoreactive for FDC markers such as CD21/CD3 5, CD23, and CNA.42. In situ hybridization for Epstein-Barr virus (EBV)-enc oded RNA was positive in all cases, remarkably highlighting the spindle cel ls and their atypia. EBV-latent membrane protein-1 was expressed commonly, albeit often focally and weakly. Therefore, inflammatory pseudotumor-like F DC tumor represents a distinctive variant of FDC tumor that differs from co nventional FDC tumor in the following aspects: marked female predominance; selective localization in intra-abdominal sites, especially the liver and s pleen; frequent presence of systemic symptoms; indolent behavior despite an intra-abdominal location; dispersed distribution of tumor cells and promin ent lymphoplasmacytic infiltration; and consistent association with EBV.