Cutaneous and Nodal Histiocytic Sarcoma: A Series of Five Cases

Abstract

Histiocytic Sarcoma (HS) is an extremely rare haematolymphoid neoplasm that exhibits morphological and immunophenotypic features indicative of histiocytic differentiation. In most cases, it is misdiagnosed as Diffuse Large B-Cell Lymphoma (DLBCL) or anaplastic large cell lymphoma. HS is a diagnosis of exclusion, necessitating extensive immunophenotypic analysis to finalise the diagnosis. Hereby, authors present a case series of five cases diagnosed as HS based on histomorphology and an extensive Immunohistochemistry (IHC) panel. A total of five cases reported as HS over a five-year period (2018 to 2023) were diagnosed at the Department of Pathology. All demographic and clinical data, as well as treatment history, were collected from the patients and their family members. Paraffin-embedded blocks were retrieved from the archive, and routine Haematoxylin and Eosin (H&E) and special stains like Periodic Acid-Schiff (PAS) were performed. Microscopy revealed sheets of round to oval tumour cells with small round nuclei, inconspicuous nucleoli, and moderately microvacuolated cytoplasm. An extended IHC panel was applied to confirm the microscopic findings. All five cases exhibited intense immunoreactivity for Leukocyte Common Antigen (LCA) and showed strong positivity for the histiocytic marker CD68, while CD163 demonstrated variable cytoplasmic positivity. Dako R antibody at a dilution of 1:100 was used for the IHC analysis. This case series aims to highlight the importance of clinical, radiological, histological, and immunohistochemical properties of this rare neoplasm for early diagnosis and proper management.

Keywords

• haematolymphoid neoplasm
• histiocytes
• malignant histiocytosis