Monitoring minimal residual disease using chromosomal translocations in childhood ALL

Clonal chromosomal abnormalities have been identified in approximately 80% of childhood ALL. In most instances the genes disrupted by these abnormalities have been identified, thus providing important insights into disease pathogenesis and normal cellular physiology. Polymerase chain reaction (PCR) amplification of fusion transcripts resulting from chromosomal translocations has emerged as a sensitive and reproducible method to monitor minimal residual disease (MRD) in childhood ALL. The measure of the initial response to therapy in patients who have achieved complete remission by morphological standards can dissect clinical heterogeneity within the genetically homogeneous childhood ALL subgroup. Moreover, MRD monitoring can be applied to predict impending relapses early. Despite notable progress with this method, several critical issues must be resolved before MRD determinations can be routinely considered in clinical decision making. This chapter will focus on the main progress and common pitfalls in the PCR detection of chromosomal translocations applied to clinical studies.