Comparative genomic hybridization in pediatric acute lymphoblastic leukemia

Prognostic value of structural chromosomal rearrangements and small cell clones with high hyperdiploidy in children with acute lymphoblastic leukemia

In this study, 107 children with acute lymphoblastic leukemia (ALL) were analysed for the presence of hyperdiploidy by cytogenetics and interphase fluorescence in situ hybridisation (I-FISH). Structural aberrations in hyperdiploid cells were investigated by multiple colour FISH (mFISH). Clones with high hyperdiploidy (>50 chromosomes) (HeH) were found in 46 patients (43%). In nine of these (20%), the abnormal clone was present in <20% of the total cell population. There was no significant difference in EFS between those patients with HeH in 2.5-20% or >20% of cells. Structural rearrangements in the HeH clone were found in 10 patients (22%). In this study, HeH karyotypes containing structural aberrations were an indication of a poor prognosis in childhood ALL.

High-resolution comparative genomic hybridisation yields a high detection rate of chromosomal aberrations in childhood acute lymphoblastic leukaemia

BACKGROUND

Cytogenetic aberrations are of prognostic significance in childhood acute lymphoblastic leukaemias and a high detection rate could improve the biological understanding and classification of these diseases.

METHODS

Bone-marrow samples from 92 children with acute lymphoblastic leukaemia were studied by high-resolution comparative genomic hybridisation (HRCGH) using dynamic standard reference intervals that enhance both specificity and sensitivity in the detection of aberrations.

RESULTS

In 80 patients (87%) HRCGH revealed a total of 405 aberrations, mostly whole chromosome gains (n = 265) and partial losses (n = 80). The 25 leukaemias with a gain of more than five whole chromosomes by HRCGH harboured only 7% of all losses. With G-band karyotyping 59 patients (64%) had aberrations. HRCGH revealed more aberrations per patient than did G-band karyotyping (median: 3 vs. 1, P = 0.005), revealed aberrations in 27 of the 34 patients for whom the G-band karyotyping failed or was found to be normal, and specifically revealed more 9p losses (21% vs. 5%, P < 0.005), 12p losses (12% vs. 2%, P < 0.05) and 17q gains (11% vs. 1%, P < 0.01). Compared to the present study, the frequency of patients with aberrant karyotypes was significantly lower in previous conventional CGH studies (64% vs. 87%, P < 0.0001), as was the rate of partial aberrations per patient (1.1% vs. 1.7, P < 0.001), particularly with fewer 6q losses, 9p losses and 17q gains detected.

CONCLUSION

HRCGH is superior to conventional CGH as an adjunct to G-band karyotyping as it detects recurrent aberrations at a significantly higher rate than both these techniques.