The incidence of hybrid acute leukaemias.

During a 4-yr period, 292 patients with acute leukaemia were studied using morphology, cytochemistry and immunologic reagents to determine the cell lineage of the leukaemia. One hundred and sixty-three cases were shown to be acute lymphoblastic leukaemia (ALL), 127 acute myeloblastic leukaemia (AML) and two cases (0.6%) were classified as hybrid acute leukaemias. One was biphenotypic in which the blast cells displayed both T-lymphoid (60% E-rosettes) and megakaryocytic markers (47% CDw41/glycoprotein IIb/IIIa antigen, 50% myeloperoxidase). The second was a bilineal acute leukaemia in which some blast cells displayed B-lymphoid (47% CD10/CALLA, 40% acid phosphatase) features and other megakaryocytic (33% coagulation factor VIII:WVf antigen)/myeloid (30% Sudan Black) features. This study suggests that hybrid acute leukaemia are rare.