摘要Objective To present a special case with the karyotype and molecular marker of acute myeloid leukemia (AML)-M2 who was induced to complete remission by all-trans retinoic acid (ATRA) alone.Methods A recently hospitalized young female patient with acute leukemia was initially diagnosed as M3 subtype based on morphological French-American-British (FAB) classification. Karyotype analysis using standard G and R banding techniques and RT-PCR were applied to further define the diagnosis. After primarily cultured bone marrow cells from the iliac aspiration were tested for in vitro induced differentiation, the patient was treated with oral all-trans retinoic acid alone, 60?mg per day until complete remission was achieved. Peripheral blood and bone marrow changes were monitored over the whole treatment course.Results The characteristic chromosomal aberration for M3, the t(15;17) reciprocal translocation, was not found while a t(8;21) translocation was verified. Furthermore, an amplified product of the AML-1/ETO fusion gene instead of the PML/RARα fusion gene was detected by RT-PCR and the diagnosis was corrected from M3 to M2. Primary cultured bone marrow cells can be fully induced to terminal differentiation after 4 days exposure to ATRA. A hematological complete remission was achieved after 40 days treatment with ATRA as a single therapeutic agent, suggesting an alternative pathway mediating ATRA-induced myeloid differentiation. Conclusion A leukemia patient with a subtype other than M3, such as M2 in this case, may also be induced to complete remission by the mechanism of ATRA-induced terminal differentiation. This implies that there may be a pathway other than PML/RARα fusion gene product which mediates ATRA-induced myeloid maturation in leukemia cells.