Myelodysplastic syndrome (MDS) often transforms into acute leukemia, usually of a myeloid phenotype. However, the transformation of MDS into acute lymphoblastic leukemia (ALL) is extremely rare. We present a case of refractory anemia with excess of blasts (RAEB) that transformed into ALL. MDS (RAEB) was diagnosed in a 68-year-old Japanese woman in August 2001. Two months later, MDS progressed to erythroleukemia (French-American-British [FAB]classification, acute myeloid leukemia [AML]-M6), and in December, 2001, she was treated with combined chemotherapy containing aclarubicin, cytarabine, and granulocyte colony-stimulating factor, which improved her clinical symptoms. However, 1 month after the chemotherapy, she developed ALL. The blasts at that time had a markedly basophilic cytoplasm with multiple cytoplasmic vacuoles, and their morphology mimicked that of ALL-L3. The blasts also expressed CD13, a myeloid marker, in addition to lymphoid markers. Southern-blot analysis revealed rearrangement of the immunoglobulin heavy chain, but no additional chromosomal abnormality characteristic of ALL-L3 was detected. The patient was treated with chemotherapy, but she developed tumor lysis syndrome and died of multiple organ failure. Although the precise mechanism of lymphoid transformation is not yet fully understood, this case clinically supports the nature of MDS as a pluripotent hematopoietic stem cell disorder.
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