OBJECTIVEMinimal residual disease (MRD) is one of the most important prognostic factors in childhood acute lymphoblastic leukemia (ALL). Flow cytometry and PCR are two common techniques for examining MRD in ALL. This study aimed to identify MRD targets by tandem application of both techniques in children with ALL.

METHODSFrom September 2001 to October 2003, 126 children with newly diagnosed ALL were enrolled on the treatment protocol ALL-XH-99. Tandem application of flow cytometry and PCR was performed to identify MRD targets in these patients.

RESULTS1. Using sets of combined antibodies, immunophenotypic expression of leukemia cells was observed in 95 of 106 B-lineage ALL cases (89.6%). Only one aberrant immunophenotype was observed in 11 cases (11.6%) and most patients with B-lineage ALL (88.4%) expressed at least two suitable targets. 2. Using PCR technique, T-cell receptor (TCR) or immunoglobulin gene rearrangements were identified in 26 of 27 patients (96.3%). Two or more monoclonal/ bi-allelic gene rearrangements were identified in 17 cases (65.4%). The majority (70%) of T-lineage ALL cases contained TCRVgammaI-Jgamma1.3/2.3. Cross-lineage TCR rearrangements were found in 57.1% of cases with B-lineage ALL. 3. Suitable MRD targets of immunophenotypic abnormalities or antigen receptor gene rearrangements were detected in 121 patients (96.0%).

CONCLUSIONSMRD targets were identified using tandem application of flow cytometry and PCR in almost of children with ALL. Cross-lineage TCR rearrangements and bi-allelic gene rearrangements were observed in many patients.