Fibroblastic/cytokeratin-positive interstitial reticular cell tumor of the spleen with indolent behavior: a case report with review of the literature.

Fibroblastic reticulum cell tumor (FRCT) is a rare dendritic neoplasm arising from fibroblastic reticulum cells (FBRCs) and exhibiting peculiar cytokeratin expression. FRCTs usually involve the lymph nodes, although they can also be encountered in the spleen and soft tissues. FRCTs are composed of mildly atypical spindle or ovoid cells, arranged in loose whorls, which express almost invariably low-weight cytokeratins, smooth muscle actin, and CD68. An admixed lymphoplasmacytic infiltrate is also frequently present in solid organ sites. The clinical picture may vary from very indolent to aggressive disease exhibiting features of malignancy, such as cytological pleomorphism, necrosis, or high mitotic rate and metastatic potential. FRCT is a challenging diagnosis, due to its rarity and deceptive cytokeratin expression. Hereafter, we revise the most recent literature regarding such condition and report the case of an extremely indolent splenic FRCT, with no features of malignancy.