Clinical significance of minimal residual disease in childhood acute lymphoblastic leukemia

Background and Methods The implications of the detection of residual disease after treatment of acute lymphoblastic leukemia (ALL) are unclear. We conducted a prospective study at 11 centers to determine the predictive value of the presence or absence of detectable residual disease at several points in time during the first six months after complete remission of childhood ALL had been induced. Junctional sequences of T-cell-receptor or immunoglobulin gene rearrangements were used as clonal markers of leukemic cells. Residual disease was quantitated with a competitive polymerase-chain-reaction (PCR) assay. Of 246 patients enrolled at diagnosis and treated with a uniform chemotherapy protocol, 178 were monitored for residual disease with one clone-specific probe (in 74 percent) or more than one probe tin 26 percent). The median follow-up period was 38 months. Results The presence or absence and level of residual leukemia were significantly correlated with the risk of early relapse at each of the times studied (P<0.001). PCR measurements identified patients at high risk for relapse after the completion of induction therapy (those with greater than or equal to 10(-2) residual blasts per 2x10(5) mononuclear bone marrow cells) or at later time points (those with greater than or equal to 10(-3) residual blasts). Multivariate analysis showed that as compared with immunophenotype, age, risk group (standard or very high risk), and white-cell count at diagnosis, the presence or absence and level of residual disease were the most powerful independent prognostic factors. Conclusions Residual leukemia after induction of a remission is a powerful prognostic factor in childhood ALL. Detection of residual disease by PCR should be used to identify patients at risk for relapse and should be taken into account in considering alternative treatment. (N Engl J Med 1998;339:591-8.) (C) 1998, Massachusetts Medical Society.