Clonal cell lineage involvement in myelodysplastic syndromes studied by fluorescence in situ hybridization and morphology.

We have used DNA fluorescence in situ hybridization (FISH) in combination with morphology to study cell lineage involvement in peripheral blood and bone marrow smears from 15 patients with myelodysplastic syndromes (MDS) and known numerical chromosomal aberrations. Eleven cases were investigated at diagnosis of MDS, and four at transformation to acute myeloid leukemia (MDS-AML). Using conventional cytogenetics, monosomy 7 was detected in nine cases, monosomy 17 in two, and trisomy 8 in five, either as a single aberration or as part of a complex clone. One case had both monosomy 7 and 17. Three biotinylated DNA probes directed against the pericentromeric region of chromosomes 7, 8 and 17, respectively, were used. Bone marrow smears were first stained with May-Grünewald-Giemsa (MGG) for morphologic evaluation, and regions of interest documented by photography. Later the same regions were targeted after hybridization, which allowed FISH analysis of selected bone marrow cells. In each patient between 267 and 921 cells (mean 453) were studied. In most cases a majority of the non-lymphoid bone marrow cells appeared to be of clonal origin, ie showed either monosomy or trisomy by FISH, while in contrast both lymphocytes and plasma cells generally were disomic, ie displayed two fluorescent spots for each probe. The percentages of clonal bone marrow cells differed greatly between patients, but in a single case there was a good agreement between the extent of granulocytic, monocytic and erythrocytic cell lineage involvement. In relation to the clinical stage of MDS, patients with more advanced disease had a significantly higher mean percentage of bone marrow blasts showing monosomy or trisomy, while disomic, possibly non-clonal cells were more frequent among the earlier forms of MDS. In the four cases of MDS-AML nearly all non-lymphoid bone marrow cells belonged to the abnormal clone. The FISH technique offers information regarding the distribution of clonal and non-clonal bone marrow cells in MDS, which might have prognostic and possibly, therapeutic implications.