Date Posted: June 10, 2026

Author/s: Ivanna Elija Ramona A. Adamos, MD; Florido A. Atibagos, MD, FPSP, MSCE and Humphrey C. Bitun, MD, FPSP

Histiocytic Sarcoma (HS) is a rare and aggressive hematopoietic neoplasm originating from the monocyte or macrophage bone marrow lineage. It has a poor outcome and pathogenesis is said to be caused by the transdifferentiation of one cell type to another of preexisting hematolymphoid tumors. Limited information both locally and internationally is due to its low incidence. Its rarity and overlap with diverse mimics makes it a clinical and diagnostic problem. This case report aims to discuss the pathologic findings of HS, explain the importance of immunohistochemistry (IHC) when dealing with poorly differentiated malignancies and review the current literature on its diagnosis. Presented here is a case report of a 41-year-old Filipino male who presented with abdominal pain and lymph node enlargement who subsequently underwent biopsy. His surgical pathology report revealed a poorly differentiated malignancy with the following considerations: hematologic malignancy and poorly differentiated carcinoma. An IHC panel (CD3, CD20, Ki67, PanCytokeratin, S100, EMA, CD68 and CD163) was performed confirming the diagnosis of histiocytic sarcoma.

Keywords:
histiocytic sarcoma, immunohistochemistry, lymph node