Augmented Consolidation Therapy Based on Minimal Residual Disease (MRD) and Analysis of the Measurement of Sequential MRD in Childhood Acute Lymphoblastic Leukemia : Children's Cancer and Leukemia Study Group of JAPAN (CCLSG), Cclsg ALL 2004 Protocol Study

BACKGROUND: Minimal residual disease (MRD) level after induction (Time Point1:TP1) and before consolidation therapy (Time Point2:TP2) has a strong impact in prediction of outcome for childhood acute lymphoblastic leukemia and it has clinical utility of a prognostic factor to stratify the risk groups in many current studies. We measured MRD levels on various time points to evaluate their prognostic significance in MRD-based augmented therapy.

PATIENTS & METHODS: From June 2004 to September 2009, we prospectively assigned 333 consecutive children with ALL, 1〜19 years of age, to receive one of three treatment protocols on the stratification based on National Cancer Institute (NCI) risk criteria. NCI standard risk:SR, NCI high risk:HR and those with a white blood cell count≧1000x10⁹ per L was defined as high-high risk:HHR. Patients were stratified again at TP2, patients with MRD level over 10^-3 were assigned to salvage arm, treated in augmented therapy. Among 333 patients, 326 were eligible and 245 were MRD quantifiable. Then, we re-evaluated those samples by RQ-PCR according to the guideline of Euro MRD. Finally 167 cases were analyzed at 7 time points of MRD quantification in the CCLSG ALL2004 study.

RESULTS: The overall 5-year event free survival (5-EFS) rate for ALL2004 was 82.5±2.1% (n=326), and 5-EFS of SR group (n=267), HR group (n=86) and HHR group (n=33) were 84.8±2.5%, 80.1±4.3% and 74.7±7.8%, respectively. In the SR group, 5-EFS of standard therapy group (n=124) with TP2 MRD<10^-3 was 87.5±3.0% and augmented therapy group's 5-EFS was 80.0±10.3% (n=15, p=0.6124). In the HR group, 5-EFS of standard therapy was 83.1±5.1% (n=54) and augmented therapy group's was 57.1±18.7% (n=7, p=0.870). In the HHR group, 5-EFS of standard therapy was 87.5±8.3% (n=16) and augmented therapy group's was 51.4±20.4% (n=7, p=0.054).

TP1, at week 7, at the end of induction, 5-year relapse free survival (5-RFS) was 87.4.% in MRD negative cases (n=115) and 58.3% in MRD positive cases (n=36), and the differences were significant. TP2,week13, during consolidation, and TP3, at week 19 or 22, and at TP4, at week 26 to 28, had significant difference on 5-RFS with cut off of both 10^-3 and 10^-4. TP7, at the end of therapy, 2 patients were MRD positive and were thought molecular relapse. Additionally, we investigated changes in MRD levels of relapsed cases (n=35). MRD remained cases (n=4), MRD late disappeared cases (n=4), and MRD converted to positivity cases (n=4) were observed.

CONCLUSIONS: The impact of predictive power of PCR MRD at TP1 and TP2 was validated, still more TP3 and TP4 were also statistically significant in CCLSG ALL2004 study. Even the patients whose final MRD level was negative could relapse, it is needed to investigate other prognostic factor except MRD.