Classifying AML Patients with Inv(16) into High-Risk and Low-Risk Relapsed Patients Based on Peritransplantation Minimal Residual Disease Determined By CBFÎ²/MYH11 Gene Expression
Authors: Zhao Xiaosu , Cao Leqing , Qin Yazhen , Zhang Xiaohui , Xu Lanping , Huang Xiaojun , Chang Ying-Jun 
Published: October 2019

Abstract
A subtype of patients with core binding factor acute myeloid leukemia (AML) is characterized by the presence of the presence of inv(16)(p13q22) and rarely by a translocation t(16;16)(p13;q22). The final genetic product is the fusion of the CBFβ gene at 16q22 to the smooth muscle myosin heavy chain (MYH11) at 16p13, which is termed as CBFβ/MYH11 fusion gene. Although this type of AML is considered a favorable cytogenetic subgroup both in NCCN guideline or ELN classification, in particular with the application of high-dose cytarabine-based consolidation chemotherapy regimens, disease relapse remains one of the most important causes leading to death, occurring in around 35% of patients. Thus, for this cohort of patients, allogeneic hematopoietic stem cell transplantation (allo-HSCT) is needed to as salvage treatment to improve the overall survival.
It has been reported that when patients achieved hematological remission, the MRD prior to transplantation (pre-MRD) has been demonstrated to be a useful parameter to predict leukemia relapse after allo-HSCT. Evaluating minimal residual disease (MRD) by real-time quantitative reverse transcriptase polymerase chain reaction (RQ-PCR) can quantify the expression level of fusion transcript at different time points along with the treatment. More recently, CBFβ/MYH11 fusion gene has been confirmed to be a good MRD marker and further screening out the patients in high-risk of relapse either during the treatment or after transplantation. However, due to the limit number of patients, there has been no studies about predictive value of CBFβ/MYH11expression after allo-HSCT.
Therefore, in this study, we attempted to investigate the impact of pre-MRD determined by RQ-PCR-based CBFβ/MYH11 gene expression on transplant outcomes of AML patients with inv(16)(p13q22) or t(16;16)(p13;q22). Besides, our previous studies has demonstrated that in compared to HLA-identical transplantation, haplo-identical allo-HSCT had superior graft-versus-leukemia (GVL) effect in AML patients with standard-risk. Thus, here we also wanted to know whether the level of CBFβ/MYH11 pretransplant could further divide this form of AML into high-risk and low-risk relapse patients before allo-HSCT.
Ninety AML patients with inv(16) in complete remission (CR) were monitored CBFβ/MYH11 transcript before and after allo-HSCT as MRD. A total of 23 patients received HLA-matched sibling donor transplantation (MSDT) and 67 patients received unmanipulated haploidentical hematopoietic stem cell transplantation (haplo-HSCT) were analyzed in this study. Patients were divided into four groups based on the value of CBFβ/MYH11 prior to transplantation (pre-MRD): with negative (group 1)/positive (group 2) pre-MRD before MSDT; with negative (group 3)/positive (group 4) pre-MRD before haplo-HSCT. The results showed that patients in group 2 had the highest cumulative incidence of relapse (2-year CIR, 40.7%), the lowest leukemia-free survival (2-year LFS, 50.8%) and the overall survival (2-year OS, 62.5%) among all four groups. The other three groups of patients had comparable CIR, TRM and OS (P>0.05). The patients were also classified into the other three groups according to CBFβ/MYH11 value of +1 month after transplantation: group 5: pre- and post-transplant MRD were both negative; group 6: the value of post-transplant MRD was lower than 0.2%; group 7: the value of post-transplant MRD was higher than 0.2%. Group 7 had the highest CIR compared to group 5 and 6 (P=0.217 & P=0.001, respectively) and the lowest LFS (P=0.072 & P=0.002, respectively), though the TRM and OS of these three groups were comparable (P>0.05). These results indicated that AML patients with inv(16) were able to be separated into high-risk and low-risk relapse groups based on peritransplant MRD determined by RQ-PCR-based CBFβ/MYH11. Haplo-HSCT might overcome the negative impact of pre-MRD on patient outcomes compared to MSDT.
Figure. Figure.

Disclosures
No relevant conflicts of interest to declare.