[Myelodysplastic syndrome in a child which developed into megakaryocytic leukemia with late appearing Ph1 chromosome and rearrangement of breakpoint cluster region].

A 3-year-old boy was referred to our hospital in September 1985, because of pancytopenia. His bone marrow was normocellular with 18% blasts, which had Auer rod and were positive for peroxidase staining. A diagnosis of refractory anemia with excess blasts in transformation was made according to FAB criteria. Chromosome analysis of bone marrow cells showed normal male karyotype. He attained complete remission with aclarubicin and BH-AC and continued it until August 1987 when pancytopenia and hypoplastic bone marrow developed. Chromosome analysis of bone marrow cells showed normal male karyotype and gene analysis revealed germ-line configuration of breakpoint cluster region (bcr). Overt leukemia developed in May 1988 when his WBC count increased to 60, 600/microliters with 91% blasts, which were negative for peroxidase staining, positive for anti-Ia and CDw 41 by cell surface analysis, and positive for ultrastructurally demonstrable platelet peroxidase. A diagnosis of megakaryocytic leukemia was made. Chromosome analysis of bone marrow cells showed 46, XY, t(9;22) (q34;q11) and gene analysis revealed rearrangement of bcr. He died in November 1988. Our results and review of literature suggest that late appearing ph1 chromosome and rearrangement of bcr may occur in a variety of hematologic malignancies and influence the course of disease.