ABSTRACT
Granulocytic sarcoma is a rare extramedullary tumor composed of immature myeloid cells. It is usually associated with leukemia or other myeloproliferative disorders but can also occur without overt hematologic diseases. The breast is an uncommon site of presentation and requires a high index of suspicion for diagnosis. We report such a case in a 45-year-old female, who presented with nontender left breast lump of 6 months' duration. A peripheral smear and bone marrow examination at that time was normal. A lumpectomy was done. An H and E diagnosis of lobular carcinoma vs. non-Hodgkin's lymphoma was entertained. Immunostains, however, revealed myeloperoxidase, naphthol AS-D chloroacetate esterase and CD43 positivity, indicating a diagnosis of granulocytic sarcoma. It appears that early initiation of systemic AML-type chemotherapy is beneficial and may delay or avert the development of AML in bone marrow and blood. Eight months later, the patient presented with an orbital mass; bone marrow and peripheral smear involvement by AML.