Clinical Impact of Minimal Residual Disease (MRD) Monitoring in AML with PML-Rara, CBFB-MYH11, and RUNX1-RUNX1T1: A Study on 600 Patients

Introduction:The cure rate in AML is dependent on patient´s (pts) age and performance, cytogenetics, early blast clearance and sustainable first complete remission. Investigation of minimal residual disease (MRD) is possible by multiparameter flow cytometry and molecular techniques. Recent findings have further depicted a broad spectrum of molecular markers in AML in 99% of pts (TCGA, NEJM, 2013). This broadens the portfolio of targets for MRD assessment and will hopefully help to better individualize treatment strategies. We here focused - as a paradigm - on the three hallmarks for molecular MRD studies in AML.

Aims: To better define the clinical impact and to suggest strategies for MRD monitoring in AML with PML-RARA, CBFB-MYH11, and RUNX1-RUNX1T1.

Patients and Methods: Between 2005 und 2015 we at diagnosis investigated 321 PML-RARA, 134 CBFB-MYH11, and 145 RUNX1-RUNX1T1 AML pts. Individual follow-up time points during their course of disease were studied in 2657, 1047, and 890 samples, respectively. Thus, the combined number of investigated samples is 4,594. Molecular techniques applied comprised quantitative real-time PCR and nested PCR. Median age in PML-RARA was 52 years (yrs) (2-86 yrs), in CBFB-MYH11 53 yrs (21-81 yrs), and in RUNX1-RUNX1T1 52 yrs (10-83 yrs). Median time between 2 investigations was 3.0 months (mo) in PML-RARA, 2.1 mo in CBFB-MYH11, and 2.8 mo in RUNX1-RUNX1T1pts (range for all 0.1-40.4 mo), respectively. All pts were treated with standard protocols according to genotype and age. Allogeneic bone marrow or stem cell transplantation was performed in 85 pts (14%). 

Results: 294/321 pts (92%) with PML-RARA achieved complete molecular remission (CMR) after a median of 2.9 mo (range: 0.8-9.7 mo). In contrast, in CBFB-MYH11 CMR was reached in 89/134 pts (66%) after a median of 7.4 mo (range: 1.6-16.8 mo), and in RUNX1-RUNX1T1 CMR was reached in 75/145 pts (51%) after a median of 4.7 mo (range: 1.0-11.5 mo). Of note, some of the CBFB-MYH11pts never reached CMR, always showing low level signals.

95% (278/294) of PML-RARApts that achieved CMR stayed in first CMR and did not relapse within a median follow-up of 32.6 mo (range: 1.2-134.5 mo). 5% (16/294) relapsed at a median interval after CMR of 8.1 mo. However, a second CMR was reached in 12/16 pts after relapse. Five of these 12 pts suffered from second relapses, whereof 4 pts achieved a third CMR. Third relapses occurred in 2/4 pts.

69/89 (78%) of pts with CBFB-MYH11 stayed in first CMR and never relapsed during a median follow-up of 10.4 mo (range: 1.6-47.1 mo). 20/89 relapsed after 4.0 mo of CMR, whereof 11 achieved second CMR. 3/11 relapsed again.

63/75 (84%) of pts with RUNX1-RUNX1T1stayed in first CMR and never relapsed during a median follow-up of 10.1 mo (range: 1.0-65.8 mo). However, 12/75 relapsed after a median time of CMR of 5.3 mo. 4/12 achieved another CMR.

In 85 patients (10 PML-RARA, 42 CBFB-MYH11, and 33 RUNX1-RUNX1T1) allogeneic bone marrow or stem cell transplantation (Tx) was performed, and 72/85 (85%) were rescued by Tx. However, two patients each with PML-RARA and RUNX1-RUNX1T1 relapsed, respectively, and 9 in CBFB-MYH11positive AML after Tx.

Patients did not experience first relapse later than 50.3 mo in CMR in PML-RARA, later than 30.7 mo in CBFB-MYH11, and later than 35.7 mo in RUNX1-RUNX1T1. Additionally, keeping periods between two MRD samplings at a maximum of 3 mo allowed the detection of nearly all cases of first relapse due to the molecular hint.

Addressing the sensitivity levels of the assays applied to bone marrow (BM) versus peripheral blood (pB) samples showed a 1.4 fold higher sensitivity for BM samples (median copies of reference gene, 13,204 vs 9,240). Due to the comparable sensitivities pB can be investigated until a first hint of relapse, followed by BM sampling for confirmation.

Conclusions: 1) MRD by molecular techniques reliably defines pts risks in AML with PML-RARA, CBFB-MYH11, and RUNX1-RUNX1T1, respectively. 2) Clinical decisions are reliable within screening intervals of 3 mo using pB. 3) Relapses in first CMR are not detected later than 50.3 mo in PML-RARA, 30.7 mo in CBFB-MYH11, and 35.7 mo in RUNX1-RUNX1T1 AML, respectively. 4) Pts after relapse can be rescued by transplantation in the majority of cases. 5) As the availability of other molecular markers in AML has dramatically increased, more individualized treatment strategies based on specific MRD monitoring are achievable in nearly every patient in the near future.