Fine-needle aspiration cytology of a liver metastasis of follicular dendritic cell sarcoma.

Follicular dendritic cell sarcoma (FDCS) is an uncommon neoplasm derived from FDCs in lymphoid tissue. Metastatic FDCS to the liver is rare. We present a case of a 65-yr-old woman who was referred to our institution 1 mo after splenectomy for FDCS of the spleen. An abdominal CT scan revealed a 2.0-cm liver lesion, which led to fine-needle aspiration (FNA) biopsy. Smears of the aspiration obtained were hypercellular showing a pleomorphic population of large oval to spindle-shaped tumor cells against a background of small mature lymphocytes, plasma cells, and necrotic debris. Tumor cells were arranged singly, in syncytial or fascicular patterns, and had a moderate amount of cytoplasm and indistinct cell borders. Nuclei had irregular nuclear membranes, finely granular to vesicular chromatin, and prominent nucleoli. Multinucleated and binucleated cells resembling Reed-Sternberg cells were noted occasionally. Mitotic figures, including atypical forms, were frequently identified. The diagnosis of "pleomorphic malignant spindle-cell neoplasm consistent with metastatic FDCS" was rendered and later confirmed by histological review and immunohistochemical staining of the subsequent liver resection specimen. Although cytological features of FDCS are characteristic, they are overlapping with those of many other tumors. We review the literature on this entity with emphasis on FNA cytomorphology, differential diagnosis, and immunohistochemical findings.