[Conversion of acute leukemia from a T-lymphoid to a myeloid phenotype]

A 7-year-old girl with an acute leukemia was reported whose blasts showed conversion from a T-lymphoid to a myeloid phenotype. At the onset of the disease, the blasts were negative for peroxidase and displayed FAB L1 morphology. Surface marker analysis revealed only CD7 antigen. Although complete remission was achieved, an extramedullary relapse was identified as having a several subcutaneous tumors 15 months later. Tumor cells showed the same marker expression as that of the blasts at the onset. After short term culture without an addition of any differentiation stimulators, the blast cells expressed CD2, CD3, CD4, CD8, and CD25 antigens. The karyotype was 46, XX, t(12; 21) (p11; q22). The intensive chemotherapy and radiation therapy were carried out, however, a hematological relapse occurred 12 months later. At this time, the blasts were strongly positive for peroxidase and expressed HLA-DR and CD33 antigens with disappearance of the CD7 antigen. Chromosome analysis revealed the additional abnormalities (del (7) (p15), -17, +der (17) t (17;?) (p13;?].