Evaluation of ProALL microRNAs in Blood Specimen for Prediction of Acute Lymphoblastic Leukemia Relapse Risk

1. Acute Lymphoblastic Leukemia Risk Based Treatment:

Children with ALL are usually treated according to risk groups defined by both clinical and laboratory features. This approach allows children with signs of historically very good outcome to be treated with modest therapy and to be spared more intensive and toxic treatment, while allowing children with a historically lower probability of long-term survival to receive more intensive therapy that may increase the ALL patients' chance of cure. Study groups use varying criteria, with a strong emphasis on minimal residual disease (MRD) measurements that quantify the number of leukemic cells that remain in the patient during and after treatment. The most widely used MRD assays are based on polymerase chain reaction (PCR) amplification of antigen-receptor genes, and on flow cytometric detection of abnormal immunophenotypes (Campana, 2010). These techniques identify the patients' specific leukemia clone in bone marrow before induction treatment and measure the number of residual leukemic cells post-induction. Two widely used examples of Risk stratification protocols are the Berlin-Frankfurt-Munster (BFM) Protocol in Europe and the Children's Oncology Group Protocol in USA. 2. Previous ProALL miR Findings:

The ProALL prototype assay microRNAs (miRNAs) (Avigad et al., 2016) were discovered by microarray analysis by hybridization of BM aspirates taken at diagnosis of 48 ALL patients to 979 different miRNAs. The down-regulated expression levels of miR-451 and miR-151-5p and the up-regulated expression level of miR-1290 associated with adverse prognostic factors.

The second study focused on measuring the three miRs in BM samples taken from B-ALL patients at diagnosis treated by the BFM protocol. ProALL miRs predicted high risk to relapse (p<0.0001, n=127). ProALL miRs were found to be an independent predictor when tested with prognostic factors known at diagnosis and when tested with PCR-MRD. Similar findings were found for patients treated by the DCOG protocol (n=32, p<0.0001). In a small feasibility study the investigators showed that ProALL miRs measured in blood correlated with ProALL miRs measured in bone marrow (Avigad et al. Mir Expression Profile of Peripheral Blood Lymphocytes Predicts Relapse in Pediatric Acute Lymphoblastic Leukemia. Blood. 2016;128:1736 - Poster presentation at ASH 2016). 3. Study Rationale:

Though MRD has greatly contributed to the substantial increase in ALL patients' survival and outcome, nearly 15% to 20% of young ALL patients eventually succumb to relapse, resulting in relapsed ALL as being the 4th most common childhood malignancy (Locatelli et al., 2012, Pui et al., 2012, Hunger and Mullighaan, 2015). Once relapse occurs only 30% to 50% of relapsed patients can be cured even with intensive chemotherapy and bone marrow transplantation (Nguyen et al. 2008 and Locatelli et al., 2012). Relapsed ALL patients with high MRD prior to hematopoietic stem cell transplantation (HSCT) have a significantly worse probability of disease-free survival 10 years after relapse treatment begins (Eckert et al., 2015). Therefore, it stands to reason that early detection of relapse before a large increase in MRD can improve relapse patients disease-free survival. Yet, many oncology groups don't incorporate monitoring in ALL treatment protocols because of the labor intensity of MRD measurement; and the invalidation of the feasibility of routine MRD monitoring. This is due to factors such as variable kinetics of leukemic cell regrowth (van Dongen et al., 2015), and that nearly 50% of ALL patients succumb to relapse from a new leukemia clone not identified at diagnosis (Choi et al., 2007). The frequency of monitoring may also be limited, especially in children, due to discomfort and practical difficulties posed by BM aspiration (Coustan-Smith E. et al., 2002). A simple predictive test for ALL in blood would increase the practicality of testing ALL patients more frequently and may eventually lead to prevention of relapse by means of preemptive treatment.