Detection and monitoring of trisomy 8 by fluorescence in situ hybridization in acute myeloid leukemia: a multicentric study.

BACKGROUND AND OBJECTIVE

The role of fluorescence in situ hybridization (FISH) in the detection and monitoring of trisomy 8 (+8) in acute myelogenous leukemia (AML) has not been defined exactly. This multicentric study was performed in order to: i) analyze the sensitivity of interphase FISH with respect to conventional chromosome analysis (CCA) in detecting +8; ii) compare the results of FISH and CCA in the quantitation of the frequency of +8-positive cells; iii) analyze the possible role of FISH in the cytogenetic follow-up of patients with +8.

DESIGN AND METHODS

One hundred and ninety-eight nonconsecutive patients with a diagnosis of AML seen at five centers over a 3-year period were studied by CCA and FISH with a chromosome 8-specific centromeric probe. Two hundred interphase cells were scored in each test and the cut-off for the recognition of +8 was set at 3%. An irrelevant pericentromeric probe was used as negative control in those cases with an apparently normal karyotype and trisomy 8 in interphase cells. FISH studies were conducted at diagnosis and, in 14 cases with +8, on 1.5 occasions during follow-up.

RESULTS

Karyotype aberrations were seen in 121 cases (61.1%), with +8 being present in 38 of them (16 as the sole aberration). Interphase FISH detected +8 in 37/38 cases; in a patient with 1/10 metaphases with +8, 2.3% interphase cells with 3 signals were seen. Fourteen additional cases with occult +8 were detected by FISH, which showed 4-22% interphase cells with three signals; 6 patients had an abnormal karyotype without +8, 3 had a normal karyotype, 5 had no analyzable mitoses. In 24 cases with > 15 analyzable metaphases, percent variations between CCA and FISH in the estimation of the size of the trisomic clone ranged between 0.4% and 51%, median value 22%. Underestimation of the percent of trisomy 8 by FISH occurred in all 10 cases with > 90% +8 metaphases. In 7/14 cases investigated sequentially, FISH detected 5-35% trisomic cells in the BM after induction therapy (4 CR, 3 PR); 4 cases relapsed with +8 at 8-15 months. The absence of +8 in remission marrows was documented in the remaining 7 cases, 4 of which relapsed at 20-32 months.

INTERPRETATION AND CONCLUSIONS

It is concluded that FISH was a valuable method in this multicentric study since it showed greater sensitivity than CCA in detecting minor clones with +8, in patients with both normal and abnormal karyotypes. The role of FISH in the cytogenetic follow-up of trisomies in AML patients may be promising.