Histiocytic Sarcoma : Introduction

Comments:
Introduction: Histiocytic sarcoma is a malignant tumor with histiocytic differentiation (based on immunophenotypic and morphologic findings). By definition, extramedullary myeloid tumors with monocytic phenotype and dendritic cell neoplasms are excluded.

Terminology: Previously used terms include malignant histiocytosis, true histiocytic lymphoma, and reticulum cell sarcoma. Before the availability of immunophenotyping and molecular genetic studies, many so-called true histiocytic lymphoma or malignant histiocytosis were in fact misdiagnosed cases of anaplastic large cell lymphoma, peripheral T-cell lymphoma, lymphomatoid papulosis, hemophagocytic syndrome (associated with T-cell or NK-cell lymphomas and viral infections such as Epstein-Barr virus), Hodgkin's lymphoma, Lennert's lymphoma, as well as hyperimmune reactions.

Sites: Lymph nodes are the most frequently involved site. Extranodal sites include skin, liver, spleen, bone, and gastrointestinal tract. Some patients develop systemic disease with multi-organ involvement, giving rise to the previously used term malignant histiocytosis. There is no involvement of peripheral blood.

This low-power scan is from a histiocytic sarcoma involving the stomach in a 43 y/o male. See the next six images for additional details.