Contrasting antigenic maturation patterns in M0-M2 versus M3 acute myeloid leukemias.

Acute myelogenous leukemia (AML) is divided into 8 FAB subgroups based on differentiation and maturation properties of the neoplastic cells. Acute promyelocytic leukemia (APL), or M3 AML, is associated with disseminated intravascular coagulation (DIC). Flow cytometric immunophenotyping differentiates among the AML subtypes. Key markers in this classification include the myeloid antigens CD13 and CD33 and the hematopoietic precursor markers CD34 and HLA-DR. The present study analyzes and compares differences in the expression of these markers in 27 M0-M2 cases and 8 M3 cases. The M0-M2 cases generally expressed all four antigens. CD13 and CD33 were positively expressed in 23 (85.2%) and 21 (77.8%) of the 27 cases, respectively. CD34 and HLA-DR were present in 25 (92.6%) and 26 (96.3%) of the 27 cases, respectively. Analysis of the M3 cases revealed a different immunophenotype as CD13 and CD33 were each positive in all 8 (100%) M3 AML cases while CD34 and HLA-DR were negative in 6 (75%) and 8 (100%) of the 8 M3 cases, respectively. In contrast to expression of the early markers CD34 and HLA-DR in the M0-M2 group, these were negative in the M3 cases which were characterized by heterogeneous CD13 and generally homogeneous and bright CD33 expression.