Fibroblastic Reticulum Cell Tumor of Spleen: A Case Report.

Fibroblastic reticulum cells (FBRCs) belong to a major subtype of stromal support cells in the lymphoid system and rarely give rise to tumors. We report a case of fibroblastic reticulum cell tumor arising in the spleen. The tumor was clinically and radiologically mistaken for a metastatic deposit in the spleen. Microscopically the tumor was composed of spindle cells arranged in fascicles and storiform pattern. The cells had oval to elongated vesicular nuclei and pale eosinophilic cytoplasm with indistinct cell borders. There were admixed inflammatory cells, including large numbers of plasma cells. The tumor cells were positive for smooth muscle actin, desmin, AE1/AE3, and MNF116. They were negative for S100, CD1a, CD21, CD23, CD34, CD31, and CD35 among other markers. The morphological features and immunoprofile of this rare tumor in comparison to the few cases reported in the literature are discussed along with the positive reaction with cytokeratins and their relationship to the smaller subset of FBRCs, the cytokeratin-positive interstitial reticulum cells in the spleen.