Tandem application of flow cytometry and polymerase chain reaction for comprehensive detection of minimal residual disease in childhood acute lymphoblastic leukemia

Children with acute lymphoblastic leukemia (ALL) with greater than or equal to 0.01% leukemic cells in the bone marrow after remission induction are a t a greater risk of relapse. The most promising methods of detecting minima l residual disease (MRD) are flow cytometric identification of leukemia-ass ociated immunophenotypes and polymerase chain reaction (PCR) amplification of antigen-receptor genes. However, neither assay can be applied to all pat ients. Moreover, both assays carry the risk of false-negative findings due to clonal evolution. The simultaneous use of both assays might resolve thes e problems, but the correlation between the methods is unknown. We studied serial dilutions of normal and leukemic cells by flow cytometry and PCR amp lification of IgH genes and found the two methods highly sensitive (one leu kemic cell among 10(4) or more normal cells), accurate (r(2) was 0.999 for flow cytometry and 0.960 for PCR by regression analysis) and concordant (R- 2 = 0.962). We then examined 62 bone marrow samples collected from children with ALL in clinical remission. In 12 samples, both techniques detected MR D levels greater than or equal to 1 in 104. The percentages of leukemic cel ls measured by the two methods correlated well (r(2) = 0.978). Of the remai ning 50 samples, 48 had MRD levels greater than or equal to 1 in 10(4). In only two samples results were discordant: 2 in 10(4) and 5 in 10(4) leukemi c cells by PCR but greater than or equal to 1 in 10(4) by flow cytometry. W e conclude that immunologic and molecular techniques can be used in tandem for universal monitoring of MRD in childhood ALL.