We performed conventional cytogenetic (CC) and interphase fluorescence in situ 
hybridization (FISH) analysis with an alpha satellite chromosome 7 specific DNA 
centromeric probe (p alpha 7t1) on bone marrow material prepared for CC in 11 
controls and 80 cases of myelodysplastic syndromes (MDS). In controls, a mean of 
4.3 +/- 1% of the 700 cells examined showed only one FISH signal for chromosome 
7, and the finding of > 6.3% (mean +2 standard deviations) of cells with one 
FISH signal was considered to indicate the presence of a clone with -7. By CC, 
clonal -7 was found in 11 patients, whereas two patients had -7 in only one 
mitose (non-clonal -7). In eight of the 11 cases of clonal -7 by CC, interphase 
FISH confirmed -7. In the remaining three patients, 5.1%, 6.3% and 18.4% 
respectively of the cells had one signal. Those three patients had, in addition 
to -7 by CC, a marker chromosome which was shown to be constituted of chromosome 
7 pericentromeric material by FISH analysis on metaphase spreads (metaphase 
FISH). Of the two patients with non-clonal -7 by CC, one had a -7 clone by 
interphase FISH whereas the other patient had normal FISH results. Five of the 
67 patients with no -7 mitose by CC had clonal -7 by interphase FISH, with one 
chromosome 7 signal in 14.4 to 39% of the cells examined. At least three mitoses 
with -7 were found in two of them by metaphase FISH. Three of the five patients 
were reexamined 12 to 17 months later: CC and metaphase FISH found no -7, 
whereas interphase FISH still showed a -7 clone. Three of the patients with 
clonal -7 by CC and by FISH were reexamined in complete hematological remission 
after intensive therapy. CC found no -7 and interphase FISH was normal in all 
three patients. Our findings suggest that interphase FISH may improve the 
detection of -7 in MDS. Conventional cytogenetics should still be performed in 
parallel to FISH, however, because of possible false negative FISH results when 
a pericentromeric chromosome 7 marker is present in patients with -7. Larger 
numbers of cases with minor -7 clones, detectable by FISH only, and longer 
follow-up in those cases will be necessary to determine the significance of this 
finding, the evolution of this minor clone, and the outcome of the patients.