Assessment of measurable residual disease (MRD) has become increasingly important in the clinical management of hematologic malignancies. While MRD testing for lymphoid malignancies — where highly sensitive flow cytometry and next-generation sequencing (NGS) of clonal B- or T-cell receptor sequences allow for broad applicability and standardization — and for chronic myeloid leukemia (CML), which uses real-time quantitative MRD polymerase chain reaction (PCR) testing for the hallmark genetic lesion BCR::ABL1, standardized and universal MRD testing for acute myeloid leukemia (AML) has been challenging due to molecular and immunophenotypic disease heterogeneity.
To this end, the most recent iteration of the European LeukemiaNet MRD Working Party recommends assessing non-acute promyelocytic leukemia AML MRD using flow cytometry (which is mutation-agnostic but has a limited sensitivity threshold of 10-3 to 10-4 in the bone marrow) or real-time quantitative or digital PCR (with a typical sensitivity of 10-4 to 10-5) for the subset of patients with mutated NPM1 or core-binding factor AML (RUNX1-RUNX1T1 or CBFB-MYH11).1 While theoretically associated with improved sensitivity and reproducabiltIy, NGS-MRD has had a more limited role in AML, with guidelines suggesting that there are insufficient data to recommend NGS-MRD as a stand-alone technique at present.1
Against this backdrop, the Hourigan laboratory at the National Institutes of Health partnered with the Center for International Blood and Marrow Transplant Research (CIBMTR) to conduct the Pre-MEASURE study. This large retrospective study, encompassing 1,075 adults with AML with known diagnostic mutations in FLT3, NPM1, IDH1, IDH2, or KIT who underwent allogeneic hematopoietic cell transplantation (HCT) in first complete remission, sought to determine and validate the prognostic significance of pre-HCT NGS-MRD on post-HCT outcomes.2 The investigators performed NGS-MRD on banked pre-HCT peripheral blood remission samples obtained from the CIBMTR and considered a variant allele fraction of 0.01% (10-4) as residual disease. Their primary finding, that pre-HCT residual mutations in FLT3-ITD and/or NPM1 by NGS-MRD were significantly associated with higher post-HCT relapse and inferior overall survival (OS), was consistent across both discovery and validation cohorts, which comprised a total of 822 patients with known FLT3-ITD and/or NPM1 mutations at diagnosis. These findings were not subtle: Among the validation cohort, the three-year post-HCT relapse rate for patients with and without pre-HCT FLT3-ITD and/or NPM1 NGS-MRD was 68% versus 21%, respectively, with an associated doubling of OS in NGS-MRD–negative patients.
The study’s secondary outcomes yielded important insights as well. First, routine flow cytometry, which was used for the majority of patients included, was insensitive for pre-HCT residual disease relative to NGS-MRD and was a poor discriminative tool for OS. Second, although residual NPM1 and/or FLT3-ITD mutations pre-HCT were associated with inferior outcomes, detection of residual IDH1, IDH2, or KIT mutations had no significant impact on post-HCT relapse. Finally, although numbers were limited, younger patients with residual NPM1 and/or FLT3-ITD mutations pre-HCT had superior outcomes with myeloablative, rather than reduced-intensity, conditioning.
In Brief
Pre-MEASURE adds to a growing literature supporting the prognostic utility of NGS-MRD in AML.3-5 This large, population-based study of hundreds of patients with AML validates pre-HCT NPM1 and/or FLT3-ITD NGS-MRD as significant biomarkers of post-HCT outcome in patients with baseline NPM1 and/or FLT3-ITD–mutated AML. It also establishes that MRD detectable at variant allele frequency ≥0.01% (10 times lower than the standard cutoff) has important clinical implications.1 Further, all NGS-MRD testing in Pre-MEASURE was performed using peripheral blood, which a number of recent reports and expert guidelines now support as a convenient and sensitive source for monitoring acute leukemia using NGS-MRD.1,6 However, despite this tremendous progress, a perplexing question remains: How do these findings translate to the clinic? Many still consider AML MRD not actionable and, therefore, not worth the cost or burden. While this may be true in some settings, NGS-MRD provides insights for HCT clinical decision-making that are currently and increasingly relevant to AML. For example, multiple reports now suggest that escalation of conditioning intensity can at least partially overcome the negative impact of pre-HCT detectable NGS-MRD.2,4 At least one randomized trial supports the use of FLT3 inhibitor therapy as post-HCT maintenance for FLT3-ITD mutated AML.7 The results of the MORPHO trial (BMT CTN 1506), which will provide data on the role of gilteritinib as post-HCT maintenance based on FLT3-ITD NGS-MRD, are eagerly awaited. Importantly, Pre-MEASURE was a prelude to the prospective multicenter Molecular Evaluation of AML Patients After Stem Cell Transplant to Understand Relapse Events (MEASURE) study (NCT05224661), which is currently enrolling patients to help establish a national standard for AML NGS-MRD. Precision medicine in AML — including personalized, precision monitoring of residual disease — is now within reach.
Competing Interests
Drs. Jeyakumar and Muffly indicated no relevant conflicts of interest.
