OBJECTIVETo evaluate the clinical significance for minimal residual disease (MRD) detection by 4 color flow cytometry in B lineage acute lymphoblastic leukemia (B-ALL).

METHODSMRD was analyzed and followed up by using two panels of 4 color antibodies, mainly CD34/CD10/CD45/CD19, in 671 consecutive bone marrow specimens and 1 cerebrospinal fluid from 98 B-ALL patients. In 26 cases of them the immunophenotyping informations at diagnosis were not available.

RESULTSOf 671 bone marrow samples, 579 were MRD negative with leukemic cells below 0.0001 and 93 were MRD positive with leukemic cells over 0.0001. Of 93 MRD positive samples, leukemic cells below 0.05 were found in 64 bone marrow samples, meanwhile in the other 29 samples leukemic cells were over 0.05. Twenty patients relapsed, 19 were bone marrow relapse and one center nerves system. Fifteen of them were found MRD positive 7 - 17 weeks before relapse including 6 patients having no immunophenotyping data at diagnosis. The percentages of leukemia cells in these 15 patients were all over 0.0001. Two relapsed patients were MRD negative in 3 and 9 months before relapse, respectively. Two relapsed after MRD monitoring stopped. If MRD level was > 0.0001 at the end of induction chemotherapy and 12 weeks of treatment, the rate of relapse was 50% (6/12), while, it was 7.5% (3/40) in MRD negative patients (P = 0.000).

CONCLUSIONRelapses can be predicted by MRD monitoring, if MRD was positive in the early phase of treatment, the risk of relapse was higher. Based on the characteristics of B cells ontogeny, MRD detection can be done independently of immunophenotypic information at diagnosis.