In Childhood B-Lineage Acute Lymphoblastic Leukemia (B-ALL) with Hyperdiploidy >50 Chromosomes, Patients with 58 to 66 Chromosomes Have 99% EFS At 6-Year Follow-up: Results of the EORTC CLG 58951 Trial

Abstract 565^FN2

Hyperdiploidy >50 chromosomes (HD>50) has long been recognized as favorable group in childhood B-ALL but there is still debate on the factors contributing to heterogeneity of prognosis observed within this entity. Better outcome has been reported for patients (pts) presenting DNA index (DI) >1.16 (Blood 1985;10:213), ≥56 chromosomes (Leukemia 1996;10:213), triple trisomies (TT) +4,+10,+17, double trisomies +4,+10 (Leukemia 2005;19:734) and trisomy 18 (Blood 2003;102:2756) but there is no consensus between the reports and these factors are differently applied in current protocols.

We studied these factors in the pts with HD>50 enrolled in the ALL 58951 trial, BFM related. HD>50 were detected by cytogenetics (karyotype/FISH) and/or flow cytometry (DI). In order to analyze the outcome of HD>50 itself, pts with recurrent unfavorable translocations t(9;22), 11q23/MLL+, with t(1;19), t(12;21) or Down Syndrome were excluded, as well as near-triploidies/duplication of hypodiploidies 30–39 chromosomes.

Pts were stratified into 4 risk groups (VLR/AR1/AR2/VHR) according to DI, Modal Number of Chromosomes (MNC), WBC, CNS/gonadal involvement, presence of VHR features (unfavorable translocations, poor response to prephase, residual disease (MRD) at the end of induction >10-2). VLR was defined as: DI>1.16 or MNC>50, WBC<10×10⁹/L, no CNS/gonadal involvement and no VHR features.

Overall Results: Out of 1651 B-lineage pts registered in the 58951 study over a 10-year period (1998-2008), a total of 541 pts had HD>50. Median age was 3 years and median WBC was 5.6×10⁹/L. After prephase, 3% (N=17) were poor responders; initial risk group distribution into VLR/AR1/AR2/VHR was 45%/47%/5%/3%. After induction, 540 (99.8%) reached complete remission, 455 of whom had an MRD evaluation: MRD<10-3 (N=416;91%), MRD <10-2 and >10-3 (N=26;6%) or MRD≥10-2 (N=13;2%). At median follow-up of 6 years, 48 pts (9%) relapsed, 22 pts (4%) died and 6 (1%) died without relapse. The 6-yr EFS was 89% (SE=1.5%).

MNC was assessed in 446 pts (82%) with successful karyotypes, MNC ranged from 51 to 66 chromosomes and peaked at 55–56; 87 pts had 51 to 53 chromosomes (HD51-53), 258 pts had 54 to 57 (HD54-57) and 101 pts had ≥58 chromosomes (HD≥58). In these 3 groups, VLR regimen was given to 16%, 50% and 64% respectively. Structural abnormalities were detected in 46% of pts and associated with all MNCs. DI, assessed in 460 pts was <1.16 (N=146), 1.16 to 1.24 (N=240) and ≥1.24 (N=104). There was no strict overlap between the HD≥58 and DI ≥1.24 groups.

Prognostic Factors: The only significant prognostic factors for EFS were MNC, DI, TT, DT and MRD.

EFS was clearly improved (p<0.001) when the MNC was ≥58 chromosomes: 6-yr EFS was 80% (HD51-53) vs 89% (HD54-57) vs 99% (HD'58). In the last group, all pts had a good response to prephase, only 3 pts had detectable MRD after induction (1pt: MRD>10-2 and 2 pts: MRD≥10-3) and only 1 pt (MNC=58) relapsed. No specific profile of chromosome gains was identified in HD ≥58 since all chromosomes contributed to tri/tetrasomies, except chromosome 1. Likewise, the higher the DI the better the outcome (p=0.01): 6-yr EFS was 83% (DI<1.16) vs 90% (DI≥ 1.16 and <1.24) vs 95% (DI ≥1.24).

TT were detected in 168 out of 468 pts, and DT in 242 out of 466 pts. There was no overlap with HD ≥58 since TT and DT were distributed from 52 to 66 chromosomes. One third of TT and of DT had MNC≥58. TT and DT were also of prognostic importance for outcome: the 6-yr EFS rate was 96% (TT) vs 86% (non-TT) (p=0.005) and 94% (DT) vs 84% (non-DT) (p=0.003). A hierarchical variable based on presence of HD≥58, TT or DT showed that HD ≥58 (N=101; 6-yr EFS: 99%) group had a better outcome than TT without HD≥58 (N=115; 6-yr EFS: 93%) and DT without HD≥58 and without +17 (N=55; 6-yr EFS: 84%) groups (p=0.04). We can infer from our results that the good outcome observed for all of the TT and DT was partially due to their association with HD '58. Consequently, the best indicator for excellent outcome was a high MNC (≥58 chromosomes).

From our 58951 trial, we can assume that among children with B-ALL and HD>50, those with ≥58 chromosomes, stand every chance of being cured. Our results stress the necessity of karyotype for identifying them since this is the only way to assess MNC. They can also be detected (less accurately) by DI (DI ≥1.24). Therefore, both MNC and DI should be used for stratifying pts in the very low risk groups.