MINIMAL RESIDUAL DISEASE ANALYSIS FOR THE PREDICTION OF RELAPSE IN CHILDREN WITH STANDARD-RISK ACUTE LYMPHOBLASTIC-LEUKEMIA

We report a largely retrospective analysis of minimal residual disease (MRD) in a cohort of 66 children suffering from acute lymphoblastic l eukaemia (ALL), All patients lacked high-risk features at diagnosis, i .e. the presenting white cell count was <50x10(9)/l, age 1-16 years an d translocations t(9;22) and t(4;11) were not present, All were treate d according to either the MRC protocols UKALL X or XI. PCR of IgH, TCR delta and TCR gamma gene rearrangements and allele-specific oligoprob ing were employed for the detection of MRD. Sensitivity was at least 1 0(-4) in 78/82 (93%) probes examined. A total of 33 patients relapsed (seven on therapy and 26 off) and 33 remain in continuing complete rem ission (CCR) (median follow-up 69 months from diagnosis), Of those who remain in CCR, MRD was present in the bone marrow in 32%, 10% and 0% at 1, 3 and 5 months into therapy respectively, This is in marked cont rast to the presence of MRD at these times in 82%, 60% and 41% of pati ents who relapsed (P<0.001, P<0.005 and P<0.005). These results provid e further evidence of a strong correlation between clearance of MRD ea rly in therapy and clinical outcome in childhood ALL.