Nodal histiocytic sarcoma mimicking metastatic carcinoma, a challenging diagnosis - Case report of an extremely rare hematolymphoid neoplasm with recent updates.

Histiocytic sarcoma (HS), a rare malignant neoplasm of hematolymphoid origin, belongs to the World Health Organization (WHO) classification of histiocytic and dendritic cell neoplasms. This rare aggressive malignancy occurs predominantly in adults and accounts for less than 1% of all hematolymphoid neoplasms. It arises from the monocytic/macrophage lineage and shares the histomorphologic and immunohistochemical features of mature tissue histiocytes. Its predominant presentation is extranodal, involving the intestinal tract, skin, and soft tissue, and it rarely presents with lymphadenopathy. The diagnosis of HS is entirely based on identifying the histiocytic lineage and the exclusion of other poorly differentiated malignancies with large pleomorphic cells like high-grade lymphomas, carcinoma, melanoma, germ cell tumors, and sarcomas. Herein, we report a case of a 61-year-old female patient who noticed a left supraclavicular swelling of 3 weeks duration, and the biopsy revealed a nodal HS. The clinicopathologic, histomorphologic, immunohistochemical, and molecular features of the disease will be further discussed.