The use of fluorescence in situ hybridization (FISH) for the purpose of repeated follow-up
examination of bone marrow samples from 38 leukemia patients was investigated. On the basis of conventional
cytogenetic analysis, patients with acute leukemia whose leukemic cells carried numerical
chromosomal aberrations were selected and followed with repetitive DNA probes that specifically
hybridize to one chromosome type. Repeated cytogenetic metaphase analyses would have been laborious
and not sensitive or quantitative enough to follow declining numbers of aberrant cells. FISH, as an interphase cytogenetic technique, provides a rapid and simple alternative with high sensitivity. Although FISH data before and after chemotherapy were in agreement with bone marrow cytology in 30
of 38 patients, discrepancies were noticed in specific cases. These could be explained by the presence of
cytogenetically distinct subclones that behave differently during treatment, the presence of differentiated
leukemic cells, changes in the chromosomal constitution caused by clonal relapse, or the fact that
a numerical aberration is found by conventional chromosome banding analysis while the target region
to which the probe is directed is still present in the nucleus as a diploid set