Minimally differentiated acute myelogenous leukemia (AML-M0) granulocytic sarcoma presenting in the oral cavity.

Acute myelogenous leukemia with minimal differentiation (AML-M0) is a rare subtype of acute leukemia in which blasts fail to show morphologic differentiation and conventional cytochemical stains and myeloid markers are negative. Acute myelogenous leukemia (AML) presents primarily with peripheral blood and/or bone marrow involvement. Presentation in extramedullary sites, including the head and neck region, is not uncommon. Acute myelomonocytic leukemia (AML-M4) and acute monocytic leukemia (AML-M5) have had the highest incidence of associated oral infiltrates. We report a case of a 58-year-old gentleman, with no prior history of acute leukemia, presenting with a solitary palatal swelling. Initial morphologic examination favored high-grade non-Hodgkin's lymphoma (NHL). Conventional cytochemical and immunohistochemical stains were negative for lymphoid and myeloid markers. Subsequent immunophenotyping via flow cytometry performed on peripheral blood and bone marrow aspirate demonstrated myeloid lineage without lymphoid differentiation, confirming the diagnosis of AML-M0.To our knowledge, this subtype of AML-M0 has not been previously reported involving the oral cavity. With absence of morphologic differentiation, and negative findings on conventional cytochemical and immunohistochemical stains, this subtype of leukemia may be misdiagnosed as non-Hodgkin's lymphoma (NHL). Flow cytometry is useful in detecting the myeloid lineage of this leukemia.