Minimal Residual Disease (MRD) Monitoring in NPM1 Mutated Acute Myeloid Leukemia (AML): Impact of Concurrent FLT3-ITD and DNMT3A Mutations on MRD Kinetics and Clinical Outcome

In a recent update on MRD monitoring in 407 NPM1 mutated (NPM1^mut) AML patients (pts) we could confirm the results from our previous study showing that achievement of RQ-PCR negativity after double induction (DI), after completion of therapy (CT) as well as during the follow-up period (FUP) is significantly associated with a lower cumulative incidence of relapse (CIR) and superior overall survival (OS) [Döhner K, Annals of Hematol; 2013;Suppl.1,92:S39]. In addition, in pts with concurrent FLT3-ITD (FLT3-ITD^mut) or DNMT3A (DNMT3A^mut) mutations, we also showed that the median NPM1^mut transcript levels after each treatment cycle were significantly higher.

To evaluate the impact of concurrent FLT3-ITD and DNMT3A^mut on MRD kinetics and clinical outcome in NPM1^mutAML pts.

For this analysis we included all pts enrolled on one of two AMLSG treatment trials [AMLHD98A (NCT00146120) n=46; AMLSG 07-04 (NCT00151242) n=199] for whom the FLT3-ITD and DNMT3A mutation status at the time of diagnosis was determined. MRD levels (ratio NPM1^mut/ABL1 transcripts x 10⁴) were detected by NPM1^mut specific RQ-PCR using TaqMan technology; the sensitivity of the assays was 10^-5 - 10^-6. DNMT3A and FLT3-ITD mutation status was assessed by standard PCR-based methods

In total, 1588 samples [bone marrow n=1564; peripheral blood n=24] from 245 NPM1^mut pts were analyzed [at diagnosis, n= 240; during therapy, n= 807; during FUP, n= 541]. FLT3-ITD and DNMT3A mutation status was available in 245/245 (FLT3-ITD^mut n=94) and in 234/245 (DNMT3A^mut n= 122) pts, respectively. Pre-treatment NPM1^mut transcript levels did not correlate with clinical characteristics, DNMT3A or FLT3-ITD mutation status and had no impact on event-free survival, relapse-free survival and OS. Multivariable analyses stratified for FLT3-ITD mutation status after DI and CT revealed RQ-PCR negativity as a significant factor for longer remission duration (hazard ratio (HR) 15.15 and 8.95, respectively) and better OS (HR 6.13 and 4.27, respectively); DNMT3A mutation status had no significant impact in these models. Subgroup analyses showed that the proportion of pts achieving RQ-PCR negativity after DI, after CT and during FUP was significantly lower in DNMT3A^mut compared to the DNMT3A wildtype pts (8.6% vs 33.3%, p=<0.001; 36,3% vs 61.9%, p=0.009; 33% vs 51%, p=0.04, respectively) whereas for FLT3-ITD^mut pts this effect was only significant after DI (8.3% vs 25%, p=0.022). Based on these findings we further investigated the impact of RQ-PCR negativity in the context of concurrent FLT3-ITD and DNMT3A mutations. After DI, there was no significant difference in CIR and OS for RQ-PCR negative pts with respect to FLT3-ITD or DNMT3A mutation status. After CT, RQ-PCR negative pts with DNMT3A^mut had a significantly higher CIR compared to DNMT3A wildtype pts (34% vs 8% at 4 years; p=0.007). This adverse prognostic impact was consistently seen during the FUP (CIR 21% vs 3% at 4 years; p=0.01); there was no difference in CIR rates between pts with and without FLT3-ITD mutations.

We demonstrate a significant correlation between the DNMT3A mutation status and the achievement of RQ-PCR negativity at all clinically relevant time points i.e. after DI, and CT, and during FUP while this strong correlation was not observed for FLT3-ITD^mut. Within the NPM1^mut RQ-PCR negative group the presence of DNMT3A^mut allows the identification of pts at high risk of relapse. Based on our findings DNMT3A mutation status should be determined in NPM1^mut pts to further refine MRD monitoring. The establishment of DNMT3A^mut specific MRD assays might provide additional information on MRD status in these pts.

Schlegelberger:Celgene: Consultancy. Lübbert:Johnson and Johnson: Advisory Board Other. Kindler:Novartis: Membership on an entity’s Board of Directors or advisory committees. Germing:Celgene: Honoraria, Research Funding. Schlenk:Novartis: Research Funding; Amgen: Research Funding; Pfizer: Honoraria, Research Funding; Chugai: Research Funding; Ambit: Honoraria; Celgene: Honoraria, Research Funding.