Prognostic Implications of the IDH1 synonymous SNP rs11554137 In Pediatric and Adult AML: a Children's Oncology Group and Southwest Oncology Group Study

Abstract 2737

Synonymous SNPs may directly impact gene function through various translational or post-translational mechanisms. Further, such “silent” SNPs in the mutational hotspots of AML-associated genes have recently been reported to carry prognostic impact. We aimed to determine the prevalence, clinical associations, and prognostic significance of a known SNP in exon 4 of IDH1, near the location of the frequently-mutated R132 codon. Diagnostic marrow specimens from 253 pediatric AML patients (treated on the COG trial AAML03P1) and 274 adult AML patients (treated on SWOG trials S9031, S9333, or S9500) were analyzed for the presence of SNP rs11554137 via direct sequencing. In the pediatric cohort (median age 9.8 years), SNP rs11554137 was present in 27 of 253 (10.7%) patients. SNP+ pediatric patients did not differ significantly from wild-type patients in terms of sex, racial distribution (African American patients accounted for 23% of SNP+ patients vs. 14% of wild-type patients, P=0.24), bone marrow blast percentage, or age distribution, except in patients aged 0–2 years, who accounted for 44% of SNP+ patients vs. 23% of wild- type patients (P=0.013). Recurrent cytogenetic abnormalities occurred with similar frequencies in both the SNP+ and wild-type pediatric populations, as did FLT3/ITD, NPMc, and CEBPA mutations. Miscellaneous cytogenetic abnormalities accounted for 33% of SNP+ patients vs. 14% of wild-type patients, P=0.033. IDH1 SNP status had no prognostic impact on survival in the pediatric cohort, as SNP+ and wild-type patients had similar rates of five-year overall survival (OS, 76% vs. 63%, P=0.50), disease-free survival (DFS, 48% vs. 53%, P=0.97), and relapse rate (RR, 39% vs. 39%, P=0.94). In the adult cohort (median age 63 years), the IDH1 SNP was present in 30 of 274 (10.9%) patients. A slight female predominance for the SNP (63% vs. 37%, P=0.052) occurred among adult patients. The SNP was more prevalent in African American patients, who accounted for 30% of the SNP+ patients vs. 7% of wild-type patients, P=0.0046. SNP+ patients also had somewhat higher diagnostic bone marrow blast percentages (medians 80% vs. 70%, P=0.025). The normal karyotype subset accounted for similar proportions of SNP+ vs. wild-type patients (42% vs. 46%, P=0.83). Notably, SNP rs11554137 was not present in adult core-binding factor AML. Miscellaneous cytogenetic abnormalities were significantly more common in SNP+ patients (46% vs. 22%, P=0.022). SNP status was not significantly associated with FLT3/ITD status when all adult patients were considered (P=0.14). However, within the normal karyotype subset, FLT3/ITD was present in 90% of SNP+ patients vs. 59% of wild-type patients (P=0.0053). SNP+ patients had somewhat poorer 5 year OS (10% vs. 18%, hazard ratio [HR]=1.17) though this difference was not statistically significant (P=0.44). Among the 142 patients who achieved complete remission (CR), however, 5-year relapse-free survival (RFS) was significantly worse for SNP+ patients (0% vs. 25%, HR = 2.89, P=0.0014). Of the 14 SNP+ patients who achieved CR, 13 relapsed and the 14^th patient died of sepsis in remission after 61 days. In multivariate analysis, after adjusting for the effects of age and cytogenetic group, SNP rs11554137 retained an independent prognostic effect (P=0.0062) regarding RFS. Notably, when FLT3/ITD status is included in multivariate analysis, SNP positivity loses independent prognostic significance (HR=1.72, P=0.18). Genome-wide expression profiling was performed on 134 pediatric AML specimens in whom IDH1 SNP status was known. By comparing SNP+ patients with wild-type patients, we derived a distinct gene-expression signature for patients with SNP rs11554137. Among the most upregulated probe sets in the SNP+ cohort were those representing PEX6 and NFYA, both of which interact with the TGF-beta/SMAD signaling network; the retinoid × receptor beta gene RXRB; and the FER gene, a tyrosine kinase critical to FLT3 signaling. The IDH1 SNP rs11554137 is present in approximately 11% of pediatric and adult AML patients, and gene expression profiling data suggests that leukemia in SNP+ patients may have unique biologic features. The SNP was an independent predictor of decreased RFS in adult AML in univariate analysis, but not in multivariate analysis when adjusting for FLT3/ITD status.