Minimal Residual Disease in Acute Myeloid Leukemia (AML) and Hematopoietic Stem Cell Transplantation (HSCT) - A Retrospective Study
Authors: Ikoma Maura Valerio , Colturato Vergílio Antônio Rensi , Marques Camila , Penitenti Marcimara , Simione Anderson João , Machado Clarisse Martins , Mauad Lenira Queiroz , de Souza Mair Pedro , de Azevedo Wellington Morais , Mauad Marcos Augusto 
Published: October 2019

Abstract
Abstract 4469
Minimal Residual Disease (MRD) is an important criterion to define risk of relapse in Acute Leukemia (AL). The most powerful methods for MRD characterization are PCR, and flow cytometry (FCM). Although PCR is more sensible that FCM, respectively 10−4 and 10−3 logs, FCM is more applicable than PCR, usually more than 80% versus less than 50% to PCR. In patients eligible for HSTC, the value of MRD is being studied and some results showed implications both in overall survival (OS) as in event free survival (EFS). The RCI seems to be influenced by the presence or absence of MRD, as well. Nowadays the most important factor that influences survival is the relapse. Then, the earlier relapse detection has a potential to improve the therapeutic results.
We presented the results of MRD before and after HSTC and its prognostic significance. Other evaluated factors were: age, acute and chronic GVHD (aGVHD and cGVHD), cell source (bone marrow, peripheral blood, cord blood), ATG use, myeloablative conditioning or not, related (RD) and unrelated donor (UD), donor gender and disease status.
Bone marrow of 112 AML patients were analyzed by FCM, since January/ 2008 until April / 2011. The evaluation was made in irregular period of time with variable number of samples by patients. They were from 1 to 61 years old. It was considered for analysis the patients that had MRD > 0,1% and < 5%. It was considered as negative result MRD < 0,1%. A dual laser FACSCalibur™ flow cytometer was used to data acquisition and analysis. Four color panels of monoclonal antibodies were chosen according the initial disease phenotype. Cell Quest Software was used for acquisition data and PAINT-A-GATE PRO and Infinicyt ™ for FMC analysis. It was done a live gate in reference markers and it was acquired a minimum of 500000 total events in each tube. Statistical analysis were performed by Kaplan Meier curves for OS e EFS and Cox regression.
It was observed statistical significance in univariate analysis related to OS the following factors: RD (64%) × UR (42%) (p = 0,002), no ATG use (64%) × ATG use (44%) × (p = 0,003%), no aGVHD (63%) (p = 0,016) × aGVHD II to IV (50%), age > 40 years old (yo) (70%), 20 to 40 yo (59%) and < 20 yo (46%) (p = 0,048), MRD after HSCT <0,1% (77%) and > 0,1% (36%) (p=0,001) (fig 1). The other factors did not show statistical significance with a negative tendency to cord blood use (p = 0,079).
To RCI, the significance was observed in: patient age < 21 yo (52%), 21 to 40 yo (30%) and > 40 yo (21%) (p=0,015); and MRD after TCTH > 0,1% (73%) × MRD < 0,1% (15%) (p = 0,000). Exerted statistical tendency: MRD < 0,1% before HSCT (p = 0,06), 1st remission (p = 0,07) and cGVHD (p = 0,08). The group of 44 patients that did not has MRD neither before or after HSCT showed OS of 85% in three years and 11% of RCI. The five morphologic relapses observed in this group suggest that a regular monitorization of MRD must be done.
The only factor that kept statistical significance in multivariate analysis was MRD > 0,1% after TCTH in RCI (p = 0,001 HR = 9,93) and for OS (p = 0,001 HR = 3,77) (Tables 1 and 2).
In conclusion, the presence of MDR > 0,1% was the only independent prognostic factor for survival and relapse in AML patients after HSCT.

Disclosures:
No relevant conflicts of interest to declare.
Table 1:OS multivariate analysis
Table 2:RCI multivariate analysis
Figure 1: OS of patients after HSCT P = 0,000