Yokota S

Tandem duplications of the FLT3 receptor gene are associated with leukemic transformation of myelodysplasia.

We recently reported an internal tandem duplication of the human flt3 receptor gene (FLT3) as a somatic mutation in 17% of acute myelogenous leukemia (AML). The present study revealed the duplication at the juxtamembrane and the first tyrosine kinase domains of FLT3 in seven of 92 (8%) patients with myelodysplastic syndrome (MDS) and AML with trilineage myelodysplasia (AML/TMDS), the diseases which may represent neoplastic changes of pluripotent stem cells. A tandem duplication of exon 11 of FLT3 was harbored by two of 58 (3%) patients with MDS and five of 34 (15%) with overt leukemia, including MDS-derived leukemia, AML/TMDS and therapy-related leukemia. Although the duplicated regions varied within exon 11 in each case, they occurred in-frame, and altered mRNA expressions were demonstrated by reverse-transcription polymerase chain reaction. Two cases of MDS with a FLT3 duplication transformed to overt leukemia within a few months. Longitudinal analyses in two other patients with leukemia revealed that the duplication was a late genetic event during the disease course; one of whom showed two independent duplications of FLT3 at the terminal therapy-resistant phase. Of seven patients with the FLT3 duplication, six had abnormal karyotypes, and four harbored a point mutation of the N-RAS and/or TP53 genes. Patients with FLT3 mutations have poor prognoses. This study uncovered the fact that the accumulation of genetic events, including FLT3 duplication, correlates with leukemic transformation from antecedent myelodysplasia and with subsequent disease progression.

Interphase Detection of BCL6/IgH Fusion Gene in Non-Hodgkin Lymphoma by Fluorescence In Situ Hybridization

We characterized a t(3;14)(q27;q32) translocation in nine patients with B-cell, non-Hodgkin lymphoma (B-NHL) by fluorescence in situ hybridization (FISH). Fluorescence in situ hybridization with immunoglobulin heavy chain (IgH) and BCL6 gene probes detected t(3;14) rapidly and accurately, including complex t(3;14) in three patients; one with t(3;12;8;14)(q27;p13;q24.1;q32) and two with t(3;?;14)(q27;?;q32). Among these nine patients, seven escaped from cytogenetic detection by our G-banding analysis. Double-color FISH with IgH (Y6) and BCL6 (cosB5-1) showed fusion of BCL6 and IgH genes on der(3)t(3;14) in all nine patients, suggesting that der(3) may play a critical role in the development of lymphoma carrying complex as well as standard t(3;14) translocations. BCL6/IgH fusion gene was also demonstrated in interphase nuclei at a frequency of 23% to 91.5% over the cut-off value in control studies (9.0 +/- 2.76%). The breakpoints assessed by FISH with two cosmid clones containing BCL6 probes, cosB5-1 and cosB5-2, were within the cluster region in seven patients including one with complex type, but were not evaluated in two patients with t(3;?;14), because of the loss of partner chromosome. Using double-color FISH with these two BCL6-specific probes, none of an additional 32 patients in whom mitotic spreads were available showed 3q27 translocations. Fluorescence in situ hybridization with IgH and BCL6 gene probes is a rapid and sensitive method to detect t(3;14) in routine cytogenetic studies.

Acute nonlymphocytic leukemia (M2) with chromosome abnormality trisomy 4 developing eight years after radiation therapy for breast cancer

SummaryWe report here the development, 8 years after radiation therapy for breast cancer, of acute nonlymphocytic leukemia (ANLL), type M2 of the FAB classification, in which trisomy 4 was detected as the only chromosomal abnormality. Simultaneous observation of cytologic and cytogenetic features of individual colonies derived from leukemic progenitor (L-CFU) and early progenitor (CFU mix) cultures in this patient revealed that all colonies examined had a normal karyotype, although the clone with trisomy 4 was predominant in the direct bone-marrow culture. These findings suggest that progenitor cells with trisomy 4 were less predominant in colony growth when stimulated by colony-stimulating factors (CSFs) than were stem cells with a normal karyotype.