Fine needle aspiration biopsy of a granulocytic sarcoma (chloroma) of the breast

A case of granulocytic sarcoma (chloroma) presenting as an isolated left breast mass in a 56-year-old woman is described. The diagnosis was initially considered from the examination of a fine needle aspiration (FNA) biopsy specimen because of the recognition of granulocytic differentiation in the cytologic material. The patients showed no peripheral blood or bone marrow evidence of leukemia. A biopsy revealed a green neoplastic tissue infiltrating the breast. Immunohistochemical study showed intracytoplasmic lysozyme, a marker for myeloid precursors, and ultrastructural examination revealed primary myeloid granulation. These findings confirmed the FNA cytologic diagnosis of granulocytic sarcoma, which should be considered when eosinophilic myelocytes are observed in aspirated material.