133 EBV-Positive Inflammatory Follicular Dendritic Cell Sarcoma with Atypical Histomorphologic Features in the Spleen: A Rare Case Report

Introduction/Objective EBV-positive inflammatory follicular dendritic cell (FDC) sarcoma is a rare indolent malignant neoplasm typically found in the liver and spleen, with occasional involvement of the colon, pancreas and mesentery. The etiology is strongly associated with EBV infection. Clinical presentation is non-specific, including anemia, hypoalbuminemia, hypergammaglobulinemia and peripheral eosinophilia. Here we present a case of splenic EBV-positive inflammatory FDC sarcoma with atypical features. Methods/Case Report The patient is a 26-year-old male, who presented with back pain, anemia and hypergammaglobulinemia. Imaging revealed a 11.5 cm splenic mass. The patient underwent splenectomy. Grossly, the spleen was markedly enlarged, measuring 19 cm with a well-demarcated 11 cm mass with cystic spaces and areas of necrosis. Microscopically, the lesion was comprised of polymorphous lymphoplasmacytic infiltrate with scattered multinucleated giant cells and ovoid stromal cells, with patchy coagulative necrosis and without mitosis. No fascicles or clusters of spindle cells were seen. The multinucleated and ovoid stromal cells were positive for EBER in situ hybridization and smooth muscle actin immunostain. Very rare ovoid cells were positive for FDC markers (CD21, CD23), and negative for ALK-1 and B/T-cell markers. Background plasma cells were polytypic by Kappa and Lambda ISH, and small lymphocytes were B- and T-cells with a predominance of CD4+ T-cells. Final diagnosis of EBV-positive inflammatory FDC sarcoma was rendered. Results NA Conclusion EBV-positive inflammatory follicular dendritic cell (FDC) sarcoma is an extremely rare tumor found predominantly in the spleen or liver. Patients with EBV-positive inflammatory FDC sarcoma often experience mild to no symptoms. Although the clinical course is indolent, comparable to low- or intermediate- grade soft tissue sarcoma, relapsing and metastatic forms have been described. Grossly, the tumor is usually high-volume and has distinct boundaries from surrounding tissues. Microscopically, it is associated with abundant infiltration of lymphoplasmacytic cells and a scattered distribution of EBV-positive spindle-shaped cells expressing FDC markers. EBV-positive inflammatory FDC sarcoma has highly variable histological morphology and expression of immunohistochemistry markers, increasing the likelihood of misdiagnosis. This case highlights this diagnostic complexity in a patient with non-specific clinical and imaging characteristics and absence of characteristic spindled FDC cells.