Granulocytic sarcoma of the small intestine.

Granulocytic sarcoma is an extramedullary tumor of myeloblasts and/or immature myeloid cells, which can develop at any anatomic site and is often a forerunner to the development of acute myelogenous leukemia. Granulocytic sarcoma of the gastrointestinal tract most frequently involves the small intestine and most often presents with abdominal pain and obstruction. Pathologists must consider granulocytic sarcoma in any mass of unknown origin with a diffusely infiltrating population of tumor cells, as the diagnosis is often initially unrecognized, especially in nonleukemic patients. Multiple ancillary modalities are available to assist pathologists in making the correct diagnosis so that appropriate therapy can be initiated.