Prognostic factors in childhood acute lymphoblastic leukemia

Approximately 80% of children and adolsecents with acute lymphoblastic leukemia (ALL) can be cured. To reduce the rate of relapses, but also to limit treatment toxicity, risk-adapted treatment has been attempted after identifying the most specific prognostic factors. In addition to clinical factors such as age and WBC, or factors of the leukemic cell such as the immunphenotype and the cytogenetics, the in vivo response to therapy has evolved as the most important predictor for relapse. The lack of specificity of most prognostic factors stimulated the search for more relevant parameters. Detection of residual disease at defined timepoints by cytomorphology can provide specific prognostic information, which allows to define new risk groups. Detection of minimal residual disease (MRD) by identifying clone-specific T-cell receptor- (TCR) or immunglobuline (Ig) gene rearrangements is currently being evaluated to extend this approach of testing the individual's sucsceptibility to therapy. The high sensitivity of the method when indicating fast clearance of leukemia might eventually spare some patients of inadequately toxic therapy. Persistent disease is an indication for treatment modification and intensification. If standardized tools are used for treatment response evaluation, logistics and quality controls are demanding but essential for the reliable conduct of such clinical studies.