Population-based study of the pattern of molecular markers of minimal residual disease in childhood and adult acute lymphoblastic leukemia: an assessment of the practical difficulty of representative sampling for trial purposes. Northern Region Haematology Group

Aberrations in DNA methylation are detectable during remission of acute lymphoblastic leukemia and predict patient outcome

AIM

Aberrant DNA methylation patterns are a hallmark of cancer, although the extent to which they underlie cancer development is unknown. In this study, we aimed to determine whether acute lymphoblastic leukemia (ALL) patients in clinical remission retained abnormal DNA methylation patters and whether these were associated with patient outcome.

MATERIALS & METHODS

We investigated CpG island methylation of genes known to exhibit hypermethylation in leukemia using quantitative pyrosequencing analysis.

RESULTS

Although methylation levels were reduced in remission samples, they remained significantly higher than those seen in healthy controls. This retained methylation was not related to low levels of residual leukemia cells still present at remission. Methylation levels were also stable (or increased) during continuous remission and significantly correlated with long-term survival in adult ALL patients.

CONCLUSION

This study determined that abnormalities in DNA methylation are retained during ALL remission and may represent a novel prognostic marker for adult ALL patients.

Adult acute lymphoblastic leukaemia

Acute lymphoblastic leukaemia (ALL) in adults is a relatively rare neoplasm with a curability rate around 30% at 5 years. This consideration makes it imperative to dissect further the biological mechanisms of disease, in order to selectively implement an hitherto unsatisfactory success rate. The recognition of discrete ALL subtypes (some of which deserve specific therapeutic approaches, like T-lineage ALL (T-ALL) and mature B-lineage ALL (B-ALL)) is possible through an accurate combination of cytomorphology, immunophenotytpe and cytogenetic assays and has been a major result of clinical research studies conducted over the past 20 years. Two-three major prognostic groups are now easily identifiable, with a survival probability ranging from <10 to 20% (Philadelphia-positive ALL) to about 50-60% (low-risk T-ALL and selected patients with B-lineage ALL). These issues are extensively reviewed and form the basis of current knowledge. The second major point relates to the emerging importance of studies that reveal a dysregulated gene activity and its clinical counterpart. It is now clear that prognostication is a complex matter ranging from patient-related issues to cytogenetics to molecular biology, including the evaluation of minimal residual disease (MRD) and possibly gene array tests. On these bases, the role of a correct, highly personalised therapeutic choice will soon become fundamental. Therapeutic progress may be obtainable through a careful integration of chemotherapy, stem cell transplantation, and the new targeted treatments with highly specific metabolic inhibitors and humanised monoclonal antibodies.

A demographic study of the clinical significance of minimal residual disease in children with acute lymphoblastic leukemia

BACKGROUND

Minimal residual disease (MRD) detected during remission might predict outcome in children with acute lymphoblastic leukemia. No population-based studies have been carried out. We studied all children with ALL presenting over 5 years within a defined population to determine its clinical importance.

PROCEDURE

Patients were investigated for the presence of unique clonal rearrangements of IgH and T-cell receptor genes. Unique patient specific probes were used to detect, by polymerase chain reaction, the presence of clonal markers indicating MRD in mononuclear cells obtained from marrow samples at 1, 3, 5, and 24 months. The effect of MRD on event-free survival was determined.

RESULTS

Seventy-seven of 120 children with ALL had informative markers and samples of remission marrow suitable for testing. Presence or absence of MRD did not significantly affect outcome. Gender (P < 0.04) and white cell count (P < 0.04) were independent prognostic factors. Analysis of only those cases with detectable MRD showed that cases with one blast per 100 mononuclear cells, or more, 28 days after starting treatment did worse than those with lower levels (hazard ratio 7.77, P < 0.02).

CONCLUSIONS

Mere presence or absence of MRD is probably too crude a measure to be useful and worse than other standard prognostic indicators. A threshold of 10(-2) blasts at 28 days might be discriminatory, but should not be over-interpreted. The number of patients available for this analysis (31) was small, the threshold and sampling points were arbitrary and any effects could be treatment regimen-specific. Large prospective studies are needed.