Abstract
We studied clinical and biological features of five cases of hybrid leukemia. Three of the five patients were classified as biphenotypic leukemia because of the coexpression of myeloid/B lymphoid markers in patients 1 (FAB M2) and 2 (FAB CMMoL) and myeloid/T lymphoid markers in patient 3 (FAB M4). Patient 4 was identified as bilineal—biphenotypic leukemia because acute myelogenous leukemia (AML) (FAB M4) and acute lymphoblastic leukemia (ALL) (FAB L1) coexisted and each population coexpressed myeloid and T lymphoid markers. Patient 5 was identified as bilineal leukemia due to the conversion from AML (FAB M1) to ALL (FAB L1) at an interval of 3 months. The Philadelphia (Ph 1) chromosome was negative in all cases. A leukemic blast colony formation using cell line 5637 conditioned medium as a stimulator was obtained in all four patients examined. Three of the five patients had been suffering from so-called stem cell disorders such as aplastic anemia in patient 2, trilineage myelodysplasia in patient 4 and refractory anemia with excess of blasts in transformation in patient 5. The pre-existing impairment of pluripotent stem cell was probably the background of these hybrid leukemia. Hybrid leukemia appears to have an inferior prognosis: an AML-directed chemotherapy resulted in a low remission rate ( 2 5 ) with a short duration of relapse free survival ( 1 2 ) and an ALL-directed chemotherapy produced no remission ( 0 3 ). Chronological phenotypic analysis revealed that hybrid features of leukemic blasts disappeared at the time of relapse in patient 1 and progression to AML in patient 2. Monitoring of lineage-associated markers should be required for the management of hybrid leukemia.
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