Residual disease in acute lymphoblastic leukemia of childhood: Methods of detection and clinical relevance

Over the last three decades, acute lymphoblastic leukemia (ALL) of childhood has turned from a once fatal condition into a disease that can be cured in about two-thirds of patients. Nevertheless, about 30% of these children relapse with a dismal prognosis. Achievement of complete remission is an essential step in successful therapy. However, patients in complete remission as defined by morphologic criteria can still harbor more than 10(9) leukemic cells. We have recently shown that residual disease is detected in most patients after completion of therapy. The amount of persistent 'indolent' disease that is actually present in a particular patient and the degree to which it must be reduced to maintain a long-term remission is largely unknown. In order to address this question, and hence to tailor efficient therapy in accordance with the needs of the individual patient, a multitude of techniques for the detection of residual disease have been developed over the last few years. The most commonly used techniques are the polymerase chain reaction (POR) assays. These sensitive assays have revolutionized this area of research. The heterogeneity of the results obtained, however, still precludes widespread clinical applicability of these techniques.