Extramedullary masses as presenting features of acute monoblastic leukemia.

Acute monoblastic leukemia is an uncommon type of non-lymphocytic leukemia that generally first manifests with signs and symptoms of bone marrow failure. This study describes four patients with acute monoblastic leukemia in whom the initial manifestations of the disorder were related to extramedullary masses. Three of the four patients were children. All patients had bone marrow involvement. The extramedullary mass lesions of acute monoblastic leukemia may be difficult to distinguish from other hematopoietic neoplasms, such as granulocytic sarcoma, malignant lymphoma and malignant histiocytosis, and nonhematopoietic tumors. Examination of the blood and bone marrow, cytochemistry, and electron microscopy are important in identifying the nature of these tumors.