[Sarcoma of the spleen with MDM2 expression].

Primary sarcomas and sarcoma metastases are a rarity in the spleen. We report on the case of a 69-year-old male patient presenting with unclear abdominal symptoms and computed tomography (CT) revealed a tumor mass in the spleen. Histologically the tumor mass predominantly showed features of a spindle cell sarcoma with lymphoid infiltrates. The expression and amplification of MDM2 could be demonstrated by means of immunohistochemistry and fluorescence in situ hybridization (FISH). Furthermore, staging examinations did not reveal indications of any other primary tumors. These preliminary findings were suggestive of a dedifferentiated liposarcoma; however, in the further diagnostic work-up the tumor showed strong expression of CD21 and CD23 and was ultimately diagnosed as a follicular dendritic cell sarcoma (FDCS). The case emphasizes that MDM2 expression represents a possible pitfall in the diagnosis of spindle cell tumors. The differential diagnostic distinction between FDCS and a dedifferentiated liposarcoma is discussed.