A case of CD68 negative histiocytic sarcoma of axilla masquerading as metastatic breast cancer.

Histiocytic sarcoma is a malignant proliferation of cells showing morphological and immunophenotypic features of mature tissue histiocytes. Most of the cases in the literature have reported CD68 positivity. We report a case of histiocytic sarcoma whose presentation mimicked a metastatic breast cancer. A 40-year-female patient presented with a 13 × 11 cm left axillary mass in close proximity to the left breast. Tru-cut biopsy from the lesion suggested the diagnosis of a lymphoid neoplasm. Complete excision of the axillary mass was done. On simple microscopy, numerous mature small lymphocytes were seen dispersed in the follicles. Immunohistochemistry revealed CD31- and CD163-positive cells, which stained negative for CD68, CD1a, cytokeratin and S100; thus, confirming the diagnosis of histiocytic sarcoma.