Adult patients with acute lymphoblastic leukemia and molecular failure display a poor prognosis and are candidates for stem cell transplantation and targeted therapies

Whole-exome sequencing in adult ETP-ALL reveals a high rate of DNMT3A mutations

Early T-cell precursor (ETP) acute lymphoblastic leukemia (ALL) is a high-risk subgroup of T-lineage ALL characterized by specific stem cell and myeloid features. In adult ETP-ALL, no comprehensive studies on the genetic background have been performed to elucidate molecular lesions of this distinct subgroup. We performed whole-exome sequencing of 5 paired ETP-ALL samples. In addition to mutations in genes known to be involved in leukemogenesis (ETV6, NOTCH1, JAK1, and NF1), we identified novel recurrent mutations in FAT1 (25%), FAT3 (20%), DNM2 (35%), and genes associated with epigenetic regulation (MLL2, BMI1, and DNMT3A). Importantly, we verified the high rate of DNMT3A mutations (16%) in a larger cohort of adult patients with ETP-ALL (10/68). Mutations in epigenetic regulators support clinical trials, including epigenetic-orientated therapies, for this high-risk subgroup. Interestingly, more than 60% of adult patients with ETP-ALL harbor at least a single genetic lesion in DNMT3A, FLT3, or NOTCH1 that may allow use of targeted therapies.

Retrospective monitoring of minimal residual disease using hairpin-shaped clone specific primers in B-cell lymphoma affected dogs

Lymphoma is one of the most common forms of cancer in dogs as it is in humans but, unlike humans, the cure rates in canines are still very low. Despite the fact that high grade B-cell lymphomas are considered to be chemotherapy responsive, almost all treated dogs ultimately relapse and die due to the residual malignant lymphocytes, namely minimal residual disease (MRD). It would be extremely valuable for clinicians to detect, monitor and quantify MRD for risk group stratification, effective treatment intervention and outcome prediction. The PCRs targeting the Ig gene rearrangements constitute one of the most reliable tools to this end. We have recently validated a method which exploits hairpin-shaped primers for quantifying MRD. In the present study, that method is conveniently used for retrospectively monitoring MRD in the peripheral blood of 8 dogs diagnosed with B-cell lymphoma who underwent chemotherapy. All dogs attained complete remission. The median disease-free interval was 254.5 days (range 63-774) while the median survival time was 313.5 days (range 143-817 days). At admission, all dogs, except one which had already been treated with prednisone, had circulating neoplastic cells. All dogs attained complete remission (CR) which was almost always matched with a complete MRD response. The persistence of MRD despite apparent CR indicated a worse prognosis and a short duration of CR. Finally, the relapse is consistently anticipated by the reappearance of MRD in the peripheral blood. The study confirmed the suitability of an MRD monitoring assay as a clinical decision-making tool.

Monitoring of minimal residual disease (MRD) is useful to predict prognosis of adult patients with Ph-negative ALL: results of a prospective study (ALL MRD2002 Study)

BACKGROUND

Allogeneic hematopoietic stem cell transplantation (HSCT) for patients with Philadelphia chromosome (Ph)-negative acute lymphoblastic leukemia (ALL) in first complete remission (CR1) is much more intensive than multi-agent combined chemotherapy, although allogeneic HSCT is associated with increased morbidity and mortality when compared with such chemotherapy. Minimal residual disease (MRD) status has been proven to be a strong prognostic factor for adult patients with Ph-negative ALL.

METHODS

We investigated whether MRD status in adult patients with ALL is useful to decide clinical indications for allogeneic HSCT. We prospectively monitored MRD after induction and consolidation therapy in adult patients with Ph-negative ALL.

RESULTS

Of 110 adult ALL patients enrolled between July 2002 and August 2008, 101 were eligible, including 59 Ph-negative patients. MRD status was assessed in 43 patients by the detection of major rearrangements in TCR and Ig and the presence of chimeric mRNA. Thirty-nine patients achieved CR1, and their probabilities of 3-year overall survival and disease-free survival (DFS) were 74% and 56%, respectively. Patients who were MRD-negative after induction therapy (n = 26) had a significantly better 3-year DFS compared with those who were MRD-positive (n = 13; 69% vs. 31%, p = 0.004). All of 3 patients who were MRD-positive following consolidation chemotherapy and did not undergo allogeneic HSCT, relapsed and died within 3 years after CR.

CONCLUSIONS

These results indicate that MRD monitoring is useful for determining the clinical indications for allogeneic HSCT in the treatment of ALL in CR1.

Measurements of treatment response in childhood acute leukemia

Measuring response to chemotherapy is a backbone of the clinical management of patients with acute leukemia. This task has historically relied on the ability to identify leukemic cells among normal bone marrow cells by their morphology. However, more accurate ways to identify leukemic cells have been developed, which allow their detection even when they are present in small numbers that would be impossible to be recognized by microscopic inspection. The levels of such minimal residual disease (MRD) are now widely used as parameters for risk assignment in acute lymphoblastic leukemia (ALL) and increasingly so in acute myeloid leukemia (AML). However, different MRD monitoring methods may produce discrepant results. Moreover, results of morphologic examination may be in stark contradiction to MRD measurements, thus creating confusion and complicating treatment decisions. This review focusses on the relation between results of different approaches to measure response to treatment and define relapse in childhood acute leukemia.

Minimal residual disease: optimal methods, timing, and clinical relevance for an individual patient

After approximately 20 years of development and after several prospective clinical trials, the detection of minimal residual disease (MRD) has emerged as part of state-of-the-art diagnostics to guide the majority of contemporary treatment programs both in pediatric and adult acute lymphoblastic leukemia (ALL). For ALL, several methods of MRD analysis are available, but 2 are widely applicable. One is based on the detection of aberrant expression of leukemia specific antigens by flow cytometry and the other one uses the specific rearrangements of the TCR or Ig genes, which can be detected by quantitative PCR in the DNA of leukemic cells. In some cases with known fusion genes such as BCR/ABL, RT-PCR can be used as a third method of identifying leukemic cells by analyzing RNA in patient samples. Clinical application of such sophisticated tools in the stratification and treatment of ALL requires reliable, reproducible, and quality-assured methods to ensure patient safety.

Has MRD monitoring superseded other prognostic factors in adult ALL?

Significant improvements have been made in the treatment of acute lymphoblastic leukemia (ALL) during the past 2 decades, and measurement of submicroscopic (minimal) levels of residual disease (MRD) is increasingly used to monitor treatment efficacy. For a better comparability of MRD data, there are ongoing efforts to standardize MRD quantification using real-time quantitative PCR of clonal immunoglobulin and T-cell receptor gene rearrangements, real-time quantitative-based detection of fusion gene transcripts or breakpoints, and multiparameter flow cytometric immunophenotyping. Several studies have demonstrated that MRD assessment in childhood and adult ALL significantly correlates with clinical outcome. MRD detection is particularly useful for evaluation of treatment response, but also for early assessment of an impending relapse. Therefore, MRD has gained a prominent position in many ALL treatment studies as a tool for tailoring therapy with growing evidence that MRD supersedes most conventional stratification criteria at least for Ph-negative ALL. Most study protocols on adult ALL follow a 2-step approach with a first classic pretherapeutic and a second MRD-based risk stratification. Here we discuss whether and how MRD is ready to be used as main decisive marker and whether pretherapeutic factors and MRD are really competing or complementary tools to individualize treatment.

Acute lymphoblastic leukemia in children: treatment planning via minimal residual disease assessment

BACKGROUND

Acute lymphoblastic leukemia (ALL) is the most common type of cancer in children and adolescents, accounting for 30% of all cases of malignancy in this age group. The cure rate of ALL is now above 80%. The clinical and biological characteristics of ALL that have been studied to date are of limited use in predicting the individual response. Newly developed methods for the assessment of minimal residual disease (MRD) are more helpful in this regard.

METHODS

Review of pertinent literature retrieved by a selective search in Medline.

RESULTS

MRD assessment has gradually been incorporated into ALL treatment planning over the past two decades. In the largest study to date of the use of MRD for this purpose, which included 3648 children with ALL, the MRD status on days 33 and 78 after the start of treatment was found to be the most important prognostic factor. The study group included 3184 patients with B-precursor ALL (leukemia consisting of immature B-lymphocytes), of whom a large subgroup (standard risk profile, 42%) had a seven-year event-free survival rate (7Y-EFS) of 91.1%; for the 6% of B-ALL patients with a high-risk profile, the cumulative rate of recurrence was 38.5 %.The remaining 464 patients had T-ALL (leukemia consisting of T-lymphocytes). The leukemia cells were eliminated more slowly overall in these patients than in those with B-ALL. Nonetheless, the T-ALL patients with a standard risk profile (16% of all T-ALL patients) had an excellent 7Y-EFS rate (91.1%), while the high-risk group (21% of all T-ALL patients) had an MRD recurrence rate of 37.7%. These findings are representative of current data from around the world on children and adults with ALL.

CONCLUSION

MRD analysis enables more accurate prediction of ALL patients' response to treatment. Risk-group stratification by MRD assessment has already brought about considerable improvement in individualized treatment planning.

Long-term follow-up of hematologic relapse-free survival in a phase 2 study of blinatumomab in patients with MRD in B-lineage ALL

Persistence or recurrence of minimal residual disease (MRD) after chemotherapy results in clinical relapse in patients with acute lymphoblastic leukemia (ALL). In a phase 2 trial of B-lineage ALL patients with persistent or relapsed MRD, a T cell-engaging bispecific Ab construct induced an 80% MRD response rate. In the present study, we show that after a median follow-up of 33 months, the hematologic relapse-free survival of the entire evaluable study cohort of 20 patients was 61% (Kaplan-Meier estimate). The hema-tologic relapse-free survival rate of a subgroup of 9 patients who received allogeneic hematopoietic stem cell transplantation after blinatumomab treatment was 65% (Kaplan-Meier estimate). Of the subgroup of 6 Philadelphia chromosome-negative MRD responders with no further therapy after blinatumomab, 4 are in ongoing hematologic and molecular remission. We conclude that blinatumomab can induce long-lasting complete remission in B-lineage ALL patients with persistent or recurrent MRD. The original study and this follow-up study are registered at www.clinicaltrials.gov as NCT00198991 and NCT00198978, respectively.

Massive evolution of the immunoglobulin heavy chain locus in children with B precursor acute lymphoblastic leukemia

The ability to distinguish clonal B-cell populations based on the sequence of their rearranged immunoglobulin heavy chain (IgH) locus is an important tool for diagnosing B-cell neoplasms and monitoring treatment response. Leukemic precursor B cells may continue to undergo recombination of the IgH gene after malignant transformation; however, the magnitude of evolution at the IgH locus is currently unknown. We used next-generation sequencing to characterize the repertoire of IgH sequences in diagnostic samples of 51 children with B precursor acute lymphoblastic leukemia (B-ALL). We identified clonal IgH rearrangements in 43 of 51 (84%) cases and found that the number of evolved IgH sequences per patient ranged dramatically from 0 to 4024. We demonstrate that the evolved IgH sequences are not the result of amplification artifacts and are unique to leukemic precursor B cells. In addition, the evolution often follows an allelic exclusion pattern, where only 1 of 2 rearranged IgH loci exhibit ongoing recombination. Thus, precursor B-cell leukemias maintain evolution at the IgH locus at levels that were previously underappreciated. This finding sheds light on the mechanisms associated with leukemic clonal evolution and may fundamentally change approaches for monitoring minimal residual disease burden.