Impact of Molecular Mutations on Treatment Response to Hypomethylating Agents in MDS

Abstract 461

Aberrant DNA methylation is a hallmark of myelodysplastic syndromes (MDS), MDS/myeloproliferative neoplasms (MDS/MPN) and secondary acute myeloid leukemia (sAML). It provides a rationale for treating these malignancies with hypomethylating agents like 5-azacitidine (AZA) and decitabine (DAC). However, treatment outcomes remain limited and heavily weighed on morphologic/cytogenetic results. The discovery of novel mutations has provided important insight into the pathogenesis of MDS and related disorders. Genes implicated in epigenetic regulation, including DNMT3A, TET2, IDH1/IDH2, EZH2, ASXL1 and UTX have been found mutated in MDS, while others have also been implicated in MDS pathogenesis. There is limited data on the predictive value of these genetic defects for treatment response and disease outcome. We hypothesized that these defects are important biomarkers predictive of response to hypomethylating agents. We studied 88 patients with MDS (RCUD=2, RARS=6, RCMD=11, MDS-U=3, RAEB-1/2=29, CMML1/2=16, MDS/MPN-U=5, RARS-T=5, AML from MDS=11) who received hypomethylating agents (AZA=53, DAC=24, both=11). The median number of cycles was 7 [range 1–35], median age was 69 years (range 42–82) and median follow-up was 18 months (range 0–76). Responses were scored according to IWG criteria. DNMT3A, TET2, IDH1/2, EZH2, ASXL1, UTX, KRAS, NRAS, CBL, RUNX1, TP53 and SF3B1 were sequenced using standard techniques. Categorical variables were analyzed using Chi-square statistics. Overall survival (OS) was analyzed using Kaplan-Meier; p-values ≤ 0.05 were considered statistically significant. Mutated patients were older than wild type (WT) cases (72 vs. 68 years, p=.01) but were well matched for marrow blast %, cytogenetic risk group and cycles of hypomethylating agents received. We found mutations in 40/88 (45%) patients. Mutations were most frequent in SF3B1 (6/11; 55%), ASXL1 (13/50; 26%), TET2 (18/88; 20%), KRAS (3/34; 9%), and DNMT3A (7/88; 8%). Less common were mutations in EZH2 (2/43; 5%), TP53 (1/23; 4%), IDH1 (4/88; 5%), IDH2 (3/88; 3%), and UTX (1/36;3%). No mutations were found in CBL, NRAS or RUNX1. Based on single mutations, overall response rate (ORR) was higher in mutated vs WT patients for DNMT3A (6/7 [86%] vs 33/81 [41%]; p=.02), ASXL1 (11/13 [85%] vs 14/37 [38%]; p=.003), and TET2 (12/18 [67%] vs. 27/70 [39%]; p=.03). All heterozygous DNMT3A mutants responded to hypomethylating agents. Differences remained significant when stratified to AZA treatment alone for DNMT3A (6/7 [86%] vs 21/56 [38%]; p=.01) and ASXL1 (9/11 [82%] vs 12/29 [41%]; p=.02) but not TET2 (6/10 [60%] vs 21/53 [40%]; p=0.22). The predictive value of combined mutations were analyzed for DNMT3A, TET2 and/or IDH1/2, showing better response to hypomethylating therapy in patients who had a mutation; ORR (mutated: 18/28 (64%) vs WT: 21/60 (35%); p=.01). This difference remained significant in patients receiving only AZA (n=53); ORR was 11/18 (61%) in mutant and 11/35 (31%) in WT patients (p=.03). No differences in ORR were noted for KRAS, EZH2 and IDH1/2 mutant and WT patients. No SF3B1 mutants responded to treatment while both patients with UTX and TP53 mutations responded. The frequency of AML evolution was also analyzed and showed no difference between mutant and WT cases for TET2 (7/18 [39%] vs 22/70 [31%];p=.52), ASXL1 (4/10 [40%] vs 11/35 [31%]; p=.61), and DNMT3A (3/7 [43%] vs 26/81 [32%];p=.56). No differences in OS and progression free survival (PFS) were noted between responders and non-responders to hypomethylating therapy (28 vs 17 mos, p=.25; 16 vs 8 mos, p=.54). Comparison of survival outcomes for mutant and WT patients showed no significant difference for DNMT3A (OS: 30 vs 21 mos, p=0.43; PFS: 20 vs 11, p=.53), ASXL1 (OS: 28 vs 22, p=.68; PFS: 16 vs 10, p=.88), and TET2 (OS: 30 vs 20 mos, p=.30). PFS was better in TET2 mutants compared to WT (19 vs 9, p=.03). No survival differences were noted between mutant and WT cases who responded to hypomethylating agents for DNMT3A (OS: 25 vs 28,p=.84; PFS: 14 vs 16, p=.78), ASXL1 (OS: 10 vs 18, p=.48; PFS: 10 vs 6, p=.76) TET2 (OS: 27 vs 16, p=.79; PFS: 18 vs10, p=.19). In conclusion, DNMT3A, ASXL1 and TET2 mutations were independently associated with a better response to hypomethylating drugs. Moreover, combined mutations in DNMT3A/TET2/IDH1/IDH2 may influence the response to hypomethylating agents, especially AZA supporting its role as a predictive biomarker in MDS treatment.