DETECTION OF UNEXPECTED CLONES OF MONOSOMY-7 IN CHILDHOOD ACUTE LYMPHOBLASTIC-LEUKEMIA USING FLUORESCENCE IN-SITU HYBRIDIZATION

The feasibility of a fluorescence in situ hybridization (FISH) techniq ue for the detection of leukemic clones with masked chromosomal aberra tion in interphase nuclei was tested in childhood acute lymphoblastic leukemia (ALL). Twenty-one cases of ALL previously studied by classica l metaphase cytogenetics were retrospectively analysed using a centrom ere-specific chromosome 7 probe. Five cases with karyotypic abnormalit ies of chromosome 7 (2 with trisomy 7, 2 with monosomy 7 and 1 with tr isomy and tetrasomy 7) showed a correlation with FISH results, whereas in five other cases monosomy 7 was found in 12-43% of cells only by F ISH. The unexpected detection of monosomy 7 in these latter ALL patien ts suggests that either these clones are quiescent or unable to enter mitosis in vitro. This suggests that FISH and metaphase cytogenetics m ust be combined whenever possible to obtain comprehensive karyotypic i nformation.