Characteristics And Clinical Relevance Of IKZF1 Aberrations In Childhood B-cell Acute Lymphoblastic Leukemia

Objective:Tostudycharacteristicsandclinicalsignificance of IKZF1 aberrations in childhood B-Cell acute lymphoblastic leukemia and reveal its clinical value as a new risk stratification indicator for B-ALL.Methods:A total of 390 children with newly diagnosed B-ALL meeting the inclusion criteria were enrolled,quantitative PCR and Sanger sequencing were employed to analyze IKZF1 aberrations,correlation between IKZF1 aberrations and clinical characteristics such as age,gender,white blood cell count,bone marrow blast,fusion gene,chromosome characteristics were statistically analyzed,the effect of IKZF1 alterations on B-ALL survivals(overall survival,event-free survival)was assessed.Results:1.The characteristics of IKZF1 gene deletion in B-ALL.Among 390 cases with newly diagnosed B-ALL,122(31.28%)were detected IKZF1 deletions.The IKZF1 aberrations were detected twenty-nine of 75(38.67%)in high-risk B-ALL cases,and 34.09%(45/132)and26.97%(48/178)in intermediate risk and low risk subgroups,respectively.Majority of the IKZF1 deletions(96.7%,108/122)were heterozygous and only 3.28%(4/122)were homozygous.Among the△IKZF1 variants,unbroken large fragment deletions involving more than one exon were present in 76.23%(93/122)and single-exon deletions in 13.93%(17/122)of the cases.The remaining were broken deletions,accounting for 9.84%(12/122).The majority(52.94%,9/17)of the single-exon deletions involved exon 1.The common unbroken large deletion variants affected either△1-8or△4-7 with frequency of 22.58%(21/93)and 16.13%(15/93),respectively.One case of△1-8 and 3 cases of△4-7 biallelic allele deletions included.Other deletion variants were rare IKZF1 deletions and observed in19.35%(18/93)of cases with B-ALL,the incidence of each deletion was less than 4%.IKZF1 deletion was common in the high-risk B-ALL than in other risk subgroups,accounting for 38.67%(29/75),particularly among those with BCR-ABL fusion gene(68.18%,15/22)and BCR-ABL-like B-ALL(42.05%,37/88).However,the incidence of IKZF1 deletions was only 29.08%(107/122)in BCR/ABL-B-ALL.Furthermore,△IKZF1 was detected in 38.5%(60/156)of other B-ALL cases.2.Mutation characteristics of IKZF1.Mutations of exon 5 and exon 8were detected in 242 cases of IKZF1 wild-type B-ALL,only three case were detection of IKZF1 mutations,two point mutations(c.1357A>C,p.S453R)and one micro-deletions were involved(c.1020-1022delGGT,p.V341del),the former is a specific single nucleotide polymorphism(SNP)rs748892029 of IKZF1.No mutations was detected in IKZF1 exon 5,but SNP site rs113962761 was detected of the downstream,with a frequency of15.29%(37/242).Furthermore,two synonymous mutations(c.1002C>A,p.Pro334Pro and c.1176C>T,p.Asn392Asn)were detected in exon 8,both were specific SNPs of IKZF1:rs61731355 and rs61731356,the incidences were 9.09.%(22/242)and 15.29%(37/242)respectively.3.Clinical characteristics of IKZF1.390 newly diagnosed B-ALL cases were divided into deleted group and non-deleted group according to the absence of IKZF1,statistically analyzed the characteristics ofage,sex and other clinical characteristics,there were no significant difference in clinical features between△IKZF1 and wild-type cases except that hemoglobin levels in cases with△IKZF1 were lower than those with a wild-type IKZF1(P=0.038).The incidence of△IKZF1 in low-risk group was significantly lower than that in non-△IKZF1 group(36.89%vs.49.43%,P=0.021),a higher frequency of△IKZF1 was noted in both hypoploid B-ALL cases and t(9;22)(q34;q11.2)positive B-ALL compared with B-ALL cases with wild-type IKZF1(7.29%vs.0.43%,P=0.001;12.94%vs.1.71%,P<0.001).However,△IKZF1 was less likely to be detected among cases with other characteristic chromosomal aberrations compared with who with wild-type IKZF1(3.23%vs.17.95%,P<0.001).In addition,△IKZF1 was significantly higher incidence in CRLF2 positive expression group compared with the non-△IKZF1 group(43.02%vs.24.76%,P=0.001);and the mortality rate was significantly higher in△IKZF1 group than that in the non-△IKZF1 group(36.45%vs.23.65%,P=0.017).4.The effect of IKZF1 aberrations on the prognosis of B-ALL.390newly diagnosed B-ALL cases were divided into deleted group and non-deleted group according to the absence of IKZF1,accounted for31.28%and 68.72%,respectively.Compared with those with wild-type IKZF1,patients with△IKZF1 had shorter overall survival(OS)(68.81%vs.87.04%,P=0.010)and event-free survival(EFS)(67.87%vs.85.47%,P=0.008).Further analysis of the correlation between△IKZF1 and prognosis revealed that common IKZF1 deletion(△1-8&△4-7)had a poor prognosis on both their overall survival and event-free survival compared with those of IKZF1 wild-type patients(OS:61.57%vs 87.04%,P=0.043;EFS:60.49%vs 85.47%,P=0.040).Similarly,the overall survival(70.72%vs.87.04%,P=0.036)and event-free survival(69.98%vs.85.47%,P=0.032)of B-ALL with rare△IKZF1 were significantly lower than that of IKZF1 wild-type group.Among rare△IKZF1 variants,patients with△2-8 were significantly less in both OS(23.8%vs.72.8%,P=0.003)and EFS(21.4%vs.72.5%,P=0.002)compared with wild-type B-ALL;but no such impact on survivals was found among cases with deletions involving either△1,△2-3 or△4-8.No statistically significant difference was found on survivals in each△IKZF1 groups.Finally,we studied the effect of△IKZF1 on the prognosis of some B-ALL subsets and found that in BCR/ABL+B-ALL,both OS and EFS showed a decreasing trend(25.64%vs.45.67%,P=0.481;20.21%vs.42.92%,P=0.430)compared with non-△IKZF1 group;but△IKZF1 had no significant effect on the survival of BCR/ABL-like B-ALL and other B-ALL;however,OS and EFS of△IKZF1 group were significantly lower than those of the non-△IKZF1group(72.96%vs.87.90%,POS=0.042;72.29%vs.86.33%,PEFS=0.038)in BCR/ABL-B-ALL.5.COX multipvariant analysis revealed that newly diagnosed WBC≥50×10~9/L,karyotypic abnormalities and IKZF1 deletion were independent adverse prognostic indicators in B-ALL.And the hazard ratio was significantly raised(HR=3.315,95%CI:1.698-6.473;P<0.001)in BCR/ABL positive B-ALL.However,gender,age,PBX1/E2A fusion gene,MLL rearrangement and CRLF2 positive expression had no significant effect on the survivals of B-ALL.Conclusion:In this study,we characterized IKZF1 aberrations in pediatric B-ALL.Our results show that△IKZF1 are more frequent in high-risk B-ALL subgroup and other B-ALL subgroups except BCR/ABL positive B-ALL and BCR/ABL like B-ALL.△IKZF1 exert negative impact on prognosis of childhood B-ALL,it is an another risk factor for B-ALL besides newly diagnosed WBC≥50×10~9/L and karyotype abnormalities,and may serve as an independent prognostic biomarker for B-ALL.