ACUTE BIPHENOTYPIC LEUKEMIA - IMMUNOPHENOTYPIC AND CYTOGENETIC ANALYSIS

The incidence of acute biphenotypic leukaemia has ranged from less tha n 1% to almost 50% in various reports in the literature. This wide var iability may be attributed to a number of reasons including lack of co nsistent diagnostic criteria, use of various panels of antibodies, and the failure to recognize the lack of lineage specificity of some of t he antibodies used. The morphology, cytochemistry, immunophenotype and cytogenetics of acute biphenotypic leukaemias from our institution we re studied. The diagnostic criteria took into consideration the morpho logy of the analysed cells, light scatter characteristics, and evaluat ion of antibody fluorescence histograms in determining whether the abe rrant marker expression was arising from leukaemic blasts or different iated bone marrow elements. Fifty-two of 746 cases (7%) fulfilled our criteria for acute biphenotypic leukaemias. These included 30 cases of acute lymphoblastic leukaemia (ALL) expressing myeloid antigens, 21 c ases of acute myelogenous leukaemia (AML) expressing lymphoid markers, and one case of ALL expressing both B- and T-cell associated antigens . The acute biphenotypic leukaemia cases consisted of four major immun ophenotypic subgroups: CD2 + AML (11), CD19 + AML (8), CD13 and/or CD3 3+ ALL (24), CD11b + ALL (5) and others (4). Chromosomal analysis was carried out in 42/52 of the acute biphenotypic leukaemia cases: a clon al abnormality was found in 31 of these 42 cases. This study highlight s the problems encountered in the diagnosis of acute biphenotypic leuk aemia, some of which may be reponsible for the wide variation in the r eported incidence of this leukaemia. We suggest that the use of strict , uniform diagnostic criteria may help in establishing a more consiste nt approach towards diagnosis of this leukaemic entity. We also sugges t that biphenotypic leukaemia is comprised of biologically different g roups of leukaemia based on immunophenotypic and cytogenetic findings.