Immunophenotyping of acute lymphoblastic leukaemia in routinely processed bone marrow biopsy specimens

Aims-To assess the value of immunophenotyping of acute lymphoblastic leukae mia (ALL) in routinely processed bone marrow trephine biopsy specimens and to establish a minimum panel of antibodies to assess lymphoid lineage and e nable differentiation from acute myeloid leukaemia. Methods-45 routinely processed bone marrow biopsy specimens (formalin fixed , paraffin embedded and mildly decalcified in EDTA) reported to contain leu kaemic infiltrates on the basis of cytomorphological and enzyne-cytochemica l analysis of bone marrow smears (22 c-ALL, 11 T-ALL, 2 B-ALL, 10 u-ALL (un classified)) were immunostained by the ABC method with a broad panel of 26 antibodies against various haemopoietic antigens. Results-Staining with antibodies directed against myeloperoxidase and lysoz yme showed that seven cases were either biphenotypic or mixed leukaemias (2 ), or of myelogenous origin (acute myeloid leukaemia (AML)-M1 (2); AML-M4 ( 2); AML-M5a (1)). Five of these seven cases had been diagnosed initially as u-ALL, Three further cases with no compact leukaemic infiltrates were excl uded. ALL was confirmed in the remaining 35 eases, Because of revised diagn oses, the total numbers of ALL subtypes changed (23 c-ALL, 8 T-ALL, 2 B-ALL , 2 u-ALL). Immunostaining of more than 10% of blast cells in at least one case was found with 19 of the 26 antibodies. The most sensitive lineage spe cific antibodies for diagnosis were found to be anti-CD10 for c-ALL (22/23) and beta F1 for T-ALL (6/8). Expression of aberrant antigens was fairly co mmon-for example, 7/23 cases of c-ALL stained with antibodies against T cel l associated antigens. Conclusions-immunohistochemical investigation of routinely processed bone m arrow biopsy specimens enables reliable detection of ALL subtypes c-ALL and T-ALL. A minimum panel of antibodies, against TdT, CD34, myeloperoxidase, lysozyme, CD10, CD79a, and CD20, and the antibody beta F1, is proposed for the immunophenotyping of acute leukaemia.