EBV-Associated Follicular Dendritic Cell Tumor of the Spleen.

Abstract

Epstein-Barr virus (EBV) expressing follicular dendritic cell proliferations in the spleen is an extremely rare but distinct variant of follicular dendritic cell tumor (FDCT). This neoplasm typically presents as an intra-abdominal mass with a predilection to involve spleen or liver with histologic features reminiscent of inflammatory pseudotumor (IP). However, in contrast to IP, this distinct FDCT consistently is associated with EBV. A subset of splenic tumors previously reported as examples of IP or inflammatory myofibroblastic tumor represent EBV-associated FDCT retrospectively. Despite morphologic similarity with IP, at least focal proliferation of follicular dendritic cells can often be demonstrated using follicular dendritic cell markers. Based on the limited published cases (Cheuk W, et al: Am J Surg Pathol , 2001; 25:721–731), these proliferations can recur and/or metastasize but in contrast to classical intra-abdominal FDCT, their clinical behavior remains indolent. We report a case of 37-year-old gentleman who presented with a four month history of left-sided abdominal and flank pain, 8 lbs weight loss over a month, and on and off night sweats during the past two years. Initial blood tests including a CBC, LDH, electrolytes, renal and liver function were all within normal limits. CT scan of abdomen and pelvis revealed a 5.5 cm in diameter solitary splenic mass with cystic and solid components (Figure 1). There was no intra-abdominal or retroperitoneal lymphadenopathy. Hepatitis panel, EBV DNA PCR and also HIV serology were all negative. The patient underwent splenectomy due to clinical impression of a lymphoproliferative disorder. Pathology: The spleen weighed 237 grams and contained a solitary, 6 cm in greatest dimension, well circumscribed tumor. Histologically, the tumor was composed of a mixed population of small lymphocytes, histiocytes, plasma cells, and variable numbers of large oval to spindle cells. The spindle cells in some foci exhibited a storiform growth pattern. Neither overt cytologic atypia nor significant increased mitotic activity was present. Flow cytometric analysis revealed no monoclonal B-cell population or abnormal T-cell proliferation. Cytogenetic analysis revealed normal 46,XY karyotype in 20 metaphases. By paraffin immunohistochemistry, the spindled cells were positive for follicular dendritic cell markers CD21, CD35 and CD23. In situ hybridization using EBV RNA (EBER) probes revealed abundant EBV RNA transcripts in the nuclei of spindled and large oval cells (Figure 2). The spindle cells were negative for S-100 and ALK protein. The systemic symptoms resolved following splenectomy with no additional treatment. Six months after splenectomy, the patient remains asymptomatic and disease free at last clinical follow up. [Display omitted] [Display omitted]