Histiocytic sarcoma involving the central nervous system: clinical, immunohistochemical, and molecular genetic studies of a case with review of the literature.

Histiocytic sarcoma (HS) is a rare disease, and there has been much confusion concerning the diagnostic criteria for this entity. Since immunohistochemical and cytogenetic techniques have become more universally available, many cases initially diagnosed as histiocytic sarcoma have been reclassified as other diseases. We describe a case of HS that presented as a single mass lesion in left occipital lobe. At autopsy the tumor also involved the meninges as a thick exudate. Histologic examination showed numerous large pleomorphic malignant cells with areas of necrosis, numerous neutrophils, and phagocytosis by tumor cells. Immunohistochemically, the tumor cells stained positively with antibodies directed against most histiocytic markers and did not stain with antibodies directed against myeloid markers, dendritic markers, CD30, ALK1, or other lymphoid markers. Molecular cytogenetic analysis showed no rearrangement [i.e. t(2;5) translocation or other variant] by fluorescence in situ hybridization. The T-cell receptor-gamma chain by multiplex polymerase chain reaction showed a polyclonal pattern. No heavy or light chain gene rearrangements were found. To our knowledge, this is the first reported autopsy case of this rare entity primarily involving the brain and meninges.