FINAL DIAGNOSIS:

GRANULOCYTIC SARCOMA

DISCUSSION:

Granulocytic sarcoma, formerly known as chloroma, is an extramedullary myeloid tumor composed of myeloblasts or myeloblasts with neutrophils. It may be an isolated occurrence or in association with acute myeloid leukemia, chronic myeloid leukemia, chronic idiopathic myelofibrosis, hypereosinophilic syndrome, or polycythemia vera. The most common sites for this tumor are the skull, paranasal sinuses, sternum, ribs vertebrae and pelvis. It may occur simultaneously with an acute myeloid leukemia, be the first evidence of a relapse after acute myeloid leukemia treatment, or precede the conventional diagnosis of a myeloid leukemia by months or years. It is generally diagnosed in two patient groups, those under 35 and those over 65 years old.

Grossly, this tumor may take on many forms depending on the host tissue. A distinctive gross finding of granulocytic sarcoma is a greenish hue on cut sections of fresh tumor. This color fades quickly in room air and is believed to be due to the presence of myeloperoxidase within the neoplastic cells.

Microscopically, the tumor commonly consists of a relatively uniform population of large cells with irregular nuclear contours arranged in sheets. These cells made be admixed within a fibrotic matrix and therefore may appear similar to a poorly differentiated lymphoma. Immunohistochemical stains for myeloperoxidase, CD43, and CD68 are usually positive and must be considered in order to avoid mistaking a granulocytic sarcoma for a poorly differentiated lymphoma as might happen if the tissue is analyzed with only a B and T cell panel alone.

Although granulocytic sarcomas are radiosensitive, systemic chemotherapy is warranted in most cases. However, specific details for therapy and prognosis is dependent on the underlying myeloid leukemia subtype.