Background: Acute leukemias co-expressing myeloid and lymphoid antigens but does not meet the criteria for biphenotypic acute leukemia (BAL) is common, however its clinical significance is not fully defined.
Methods: In this study, clinical features of 68 co-expressing (myeloid and lymphoid) acute leukemias diagnosed between January 2000 and December 2006 were studied and compared with those of a control group of patients (pure AML or ALL).
Results: Age, gender, initial Lactate dehydrogenase (LDH) level and cytogenetics were not different between the co-expressing group and the control group. But, the initial bone marrow blast percent was significantly higher in the co-expressing group (70% vs. 54.5%, P=0.003). Fifty five percent (16/29) of ALL and 30% (52/172) of AML patients showed myeloid and lymphoid markers concomitantly. The lymphoid antigen positive AML (Ly+ AML) patients showed significantly shorter survival rates than pure AML patients (4 year survival rate, 17.6% vs. 45.6%, P=0.002). However hematopoietic stem cell transplantation (HST) abrogated the difference (4 year survival rate, 54.7% vs. 50.6%, P=0.894). In ALL patients, survival rate was not affected by myeloid antigen co-expression (4 year survival rate 26.1% vs. 20%, P=0.954).
Conclusion: Co-expression of lymphoid markers in AML should be regarded as a poor prognostic factor and more aggressive treatment such as HST should be considered. (Korean J Hematol 2009;44:67-73.)

Keywords: Acute leukemia, Immunophenotyping, Co-expression, Prognosis