Background: The recent advances in flow cyromstric technology and the development of monoclonal antibodies have led to the important insights into the cell lineage and
maturation stage of leukemia. The increassd use of immunophenotyping in acute leukemla revealsd the unusual anigen expression and biclonal or biphenotypic acute
mixed lineage leukemia(AMLL). However, the data on their frequency and prognostic significance are still conflicting.
Methods: The immunophenotyping of leukemlc cells(HLA-OR, CD10, CDl9, CD20, CD22, CD3, CD5, CD7, CDl3, CD33, CD6l, TdT, cytoplasmic lg, surface lg) was performed by flow cytometry in 115 cases of acute leukemia between January 1994 and August 1996. Double-color immunofluorescent staining was peformsd in the cases expressing unusual antigens.
Results: 51 cases(44.3%) of 115 acute leukemias showed unusual antigens exprsssion.
These included 27 cases(38.6%) of 70 AML, 13 cases(43.3%) of 30 B-lineage ALL, 4 cases(50%) of 8 T-LL and 7 AMLL cases(6.l%) of 115 acute leukemias. CD7(28.6%) and CDl9(11.4%) are expressed in AML, and CDl3(36.7%) and CD33(26.7%) are expressed in ALL. Among 7 cases of AMLL, we could obtain the clinical data of 5 cases. The 4 cases of 5 AMLL failed to respond to induction chemotherapy or died before or during induction chemotherapy, and only one case showed partial remission.
Conclusion: The unusual antigen expressions of acute leuksmic cells are frequently observed, and the identification of relatively rare AMLL is very important, because AMLL showed poor response to the chemotherapy.

Keywords: Acute leukemia, Immunophenotyping, Unusual antigen expression