Granulocytic sarcoma presenting as a giant breast tumor in a pregnant woman: a case report.

We report a case of granulocytic sarcoma (chloroma) presenting as a giant breast tumor in a pregnant woman with no history of leukemia. The case was initially diagnosed as medullary carcinoma on a biopsy specimen and a modified radical mastectomy was performed. The diagnosis of granulocytic sarcoma requires the pathologist's high index of suspicion. The presence of immature eosinophils was an important clue. Leder's chloroacetate esterase stain; immunostaining for myeloperoxidase, CD34, CD43, CD68, and lysozyme; and ultrastructural finding of cytoplasmic lysosomal granules and Auer bodies all aided in confirming the diagnosis. It is imperative to recognize granulocytic sarcoma to avoid unnecessary surgery. Granulocytic sarcoma should be included in the differential diagnosis of breast tumors, especially in tumors with diffuse proliferation of small tumor cells.