A “positive” or “negative” MRD test result indicates whether measurable disease is detected above certain thresholds that may vary by test and laboratory. It is important to recognize that a negative MRD result does not necessarily indicate eradication of disease, but rather represents disease below the test threshold in the tested sample, and patients may still experience relapse.

ELN identifies multiparametric flow cytometry (MFC) and quantitative polymerase chain reaction (qPCR) among useful methods suitable for detecting MRD. Recently, innovative techniques such as digital PCR (dPCR), next-generation sequencing (NGS), and next-generation flow cytometry (NGF) have also been applied in the detection of MRD.

In the study by Yilmaz et al., it was seen that earlier MRD negativity in Ph(-) B-ALL was associated with higher survival. The best results were obtained with Flow Cytometry MRD negativity after the 1st cycle (i.e. CR time). The 3-year relapse rate in early MRD negativity was still approximately 25%.

Short NJ et al investigated the effect of CMR in Ph (+) B ALL. In 85 Ph+ ALL patients who were treated with Hyper-CVAD plus TKI and did not undergo HSCT in CR1, the median OS was 127 months in the group achieving CMR; OS was 38 months in those without CMR (P=0.009). CMR at 3 months was seen as the only prognostic factor for OS. In the study by Sasaki K et al. evaluating the effect of TKI selection on achieving 3-month CMR; 84 Ph+ ALL patients were treated with Hyper-CVAD plus TKI and CMR was achieved at 3 months. 5-year OS was found to be 84% with ponatinib. 5-year OS was found to be 60-65% with other TKIs. Ponatinib treatment was the only prognostic factor for PFS or OS. Ghobadi A et al found no benefit from allogeneic SCT in patients with Ph+ ALL who achieved CMR.

Short NJ et al. compared the correlation and prognostic impact of NGS MRD and MFC MRD in Ph(-) ALL. NGS MRD (-) 5-year OS: 90%; NGS MRD (+) 5-year OS: 61%; MFC MRD (-) NGS MRD (+) 5-year OS: 62% were seen. 46% of the MFC MRD (-) group was NGS MRD (+).

Blinatumomab for MRD in B-Cell ALL showed MRD negativity rate = 78% after 1 cycle in BLAST Study.

Pulsipher MA et al viewed pretransplantation NGS MRD status as prognostic in pediatric ALL. Prospective follow-up for posttransplantation MRD was superior with NGS. Liang EC et al assessed NGS MRD up to 1 year after SCT for 139 patients after allogeneic SCT.

Muffly L et al evaluated the correlation of NGS MRD with Peripheral Blood and Bone Marrow. Strong correlation (r=0.87; P<0.0001) was seen between PB and BM NGS MRD. MRD was detected in PB in 100% of those who relapsed after SCT and in 85% of those who relapsed after CAR T.

Pulsipher MA et al. study, MRD assessment after CAR T Cell for ALL was considered prognostic. NGS-detectable MRD after tisagenlecleucel was independently predictive of EFS and OS in multivariate analysis.

Short NJ et al evaluated the effect of NGS MRD for IG/TR in Ph+ ALL. The study enrolled adults with Ph+ ALL receiving first-line therapy. Disagreements between MRD assessment by PCR and MRD assessment by NGS are relatively common. RT-PCR for BCR::ABL1 is not prognostic in patients who achieve NGS MRD negativity. Ph+ ALL patients who achieve NGS MRD negativity have good outcomes regardless of PCR response.

Flow cytometry in T-ALL has been validated in T ALL, including ETP. Good agreement between bone marrow and peripheral blood. NGS has not been validated in T ALL because the cells have not yet undergone a TCR rearrangement.

In first-line ALL, MRD from bone marrow should be measured after the end of induction, during early consolidation (after approximately 3 months of therapy), and then approximately every 3 months for at least 3 years (5 years for patients with Ph-positive ALL in first remission who do not undergo HSCT). In patients undergoing HSCT, MRD should be assessed immediately before HSCT; serial MRD measurements should be performed after HSCT (approximately every 3 months).”