Minimal residual disease in leukemia

Minimal residual disease (MRD) is a major issue in the monitoring and treatment of acute leukemia, since cure requires the elimination of all leukemia cells. Current strategies to eradicate MRD involve either an intensification of therapy to all patients or attempts to identify patients who need more therapy, as based upon disease characteristics at diagnosis. A number of groups have now developed polymerase chain reaction (PCR)-based techniques for detecting and quantifying low numbers of leukemia cells and a number of features potentially important for leukemia biology and treatment are emerging. These include: the recognition that quantification is more informative than detection the level of disease at the end of induction strongly predicts long term outcome the progression of leukemia in patients who relapse during treatment is quite slow and relapsing disease can be detected in the marrow for many months before clinical relapse surprisingly high levels of MRD can be detected in blood, at levels which are likely to provide valuable clinical information the Philadelphia chromosome is associated with drug resistance in childhood but not adult ALL subpopulations of drug-resistant cells are already present in many patients at diagnosis. It is possible that this new information can be used to test new approaches to treatment and this may soon be undertaken in a co-operative trial within Australasia.