Histiocytic sarcoma (HS) is a rare hematopoietic malignancy originating from the monocyte/macrophage bone marrow lineage. HS can occur in isolation or in association with other hematological neoplasms such as non-Hodgkin lymphoma (NHL), myelodysplasia, or acute leukemia. Clinically, HS can affect lymph nodes, gastrointestinal tract, skin, bone marrow, and spleen as well as the central nervous system. Most cases of HS follow an aggressive clinical course, with most patients dying of progressive disease within one year of diagnosis.