Minimal residual disease (MRD), where leukemic cell levels are lower than the morphologic detection threshold, is the most important prognostic factor for acute lymphoblastic leukemia (ALL) relapse during first-line chemotherapy treatment and is standard of care in treatment monitoring and decision making. Limited data are available on the prognostic value of MRD response after relapse. We evaluated the relationship between MRD response and outcomes in blinatumomab-treated adults with relapsed/refractory (R/R) B-cell precursor ALL. Of 90 patients with complete remission (CR) or CR with partial hematologic recovery (CRh), 64 (71.1%) achieved a complete MRD response (no detectable individual rearrangements of immunoglobulin/T-cell receptor genes by polymerase chain reaction [PCR] at a minimum sensitivity level of 10-4). Eleven patients had MRD <10-4. Therefore, overall, 75 (83.3%) experienced an MRD response (no detectable MRD or detectable MRD) measured by PCR within the first 2 treatment cycles. Overall survival (OS) and relapse-free survival (RFS) were significantly longer in patients who achieved CR/CRh and MRD response (median, 20.6 and 9.0 months, respectively) compared with CR/CRh patients without MRD response (median, 12.5 and 2.3 months, respectively). In conclusion, longer durations of OS and RFS associated with MRD response support the value of achieving MRD response and its use as a prognostic factor for blinatumomab treatment in R/R ALL. This trial was registered at www.clinicaltrials.gov as #NCT01466179.

Adults with relapsed/refractory acute lymphoblastic leukemia have an unfavourable prognosis, which is influenced by disease and patient characteristics. To further evaluate these characteristics, a retrospective analysis of 1,706 adult patients with Ph-negative relapsed/refractory B-precursor acute lymphoblastic leukemia diagnosed between 1990-2013 was conducted using data reflecting the standard of care from 11 study groups and large centers in Europe and the United States. Outcomes included complete remission, overall survival, and realization of stem cell transplantation after salvage treatment. The overall complete remission rate after first salvage was 40%, ranging from 35%-41% across disease status categories (primary refractory, relapsed with or without prior transplant), and was lower after second (21%) and third or greater (11%) salvage. The overall complete remission rate was higher for patients diagnosed from 2005 onward (45%, 95% CI: 39%-50%). One- and three-year survival rates after first, second, and third or greater salvage were 26% and 11%, 18% and 6%, and 15% and 4%, respectively, and rates were 2%-5% higher among patients diagnosed from 2005. Prognostic factors included younger age, longer duration of first remission, and lower white blood cell counts at primary diagnosis. This large dataset can provide detailed reference outcomes for patients with relapsed/refractory Ph-negative B-precursor acute lymphoblastic leukemia. clinicaltrials.gov identifier: 02003612.

Chromosomal rearrangements are initiating events in acute lymphoblastic leukaemia (ALL). Here using RNA sequencing of 560 ALL cases, we identify rearrangements between MEF2D (myocyte enhancer factor 2D) and five genes (BCL9, CSF1R, DAZAP1, HNRNPUL1 and SS18) in 22 B progenitor ALL (B-ALL) cases with a distinct gene expression profile, the most common of which is MEF2D-BCL9. Examination of an extended cohort of 1,164 B-ALL cases identified 30 cases with MEF2D rearrangements, which include an additional fusion partner, FOXJ2; thus, MEF2D-rearranged cases comprise 5.3% of cases lacking recurring alterations. MEF2D-rearranged ALL is characterized by a distinct immunophenotype, DNA copy number alterations at the rearrangement sites, older diagnosis age and poor outcome. The rearrangements result in enhanced MEF2D transcriptional activity, lymphoid transformation, activation of HDAC9 expression and sensitive to histone deacetylase inhibitor treatment. Thus, MEF2D-rearranged ALL represents a distinct form of high-risk leukaemia, for which new therapeutic approaches should be considered.