The Outcome of Low-Risk Childhood B-Cell Precursor ALL Treated with the Japan Association of Childhood Leukemia Study (JACLS) ALL-02 Trial

Background: It is important to establish proper intensity of chemotherapeutic regimen for low risk group of childhood B-precursor ALL (BCP-ALL) to avoid late effects. For this purpose, in Japan Association of Childhood Leukemia study (JACLS) ALL-02 clinical trial, we defined standard risk (SR) group as the patients ranged from 1 to 10 years showing white blood cell (WBC) count of less than 10,000/μL at the diagnosis without predonisolone poor responder, t(4;11), t(1;19) and CNS3 to treat with less intensive chemotherapy (JACLS ALL02 SR protocol). Herein, we report the outcome of JACLS ALL02 SR protocol and analyzed prognostic factors to identify super low risk group which is curable by less intensive chemotherapy.

Patientss and treatment: JACLS ALL02 SR protocol consisted of early phase therapies for total 4 months including an induction therapy using vincristine (VCR), steroids, pirarubicin (THP-ADR), and L-asparaginase (L-asp) for 4 weeks, a consolidation therapy using cyclophosphamide and a combined administration of cytarabine and dexamethasone (DEX) or 6-mercaptopurine (6-MP), a sanctuary therapy with only two cycles of high-dose methotrexate (MTX) of 3g/m², one course of 4 drugs re-induction therapy and maintenance phase with 6-MP and oral MTX combined with VCR and PSL every 5 weeks by the end of the second year. In addition, total of 12 times of triple intrathecal therapy were administered by the end of the first year. Estimation of event free survival (EFS) and overall survival (OS) was performed using the Kaplan-Meier method and the differences were compared using the log-rank test. Multivariate analysis was performed using a Cox regression model.

Results: 1252 newly diagnosed ALL patients were enrolled from April 2002 to May 2008 in JACLS ALL02 clinical trial, which include 388 patients (192 males and 196 females) in SR group (31.0%). The median age at diagnosis was 4.2 years (range, 1.0 to 9.9 years) and the median WBC count was 3,700/μL (range, 370 to 9,984 /μL). The median follow-up time was 6 year and 5 months. 4y / 8y EFS and OS (±SE) of the SR group are 91.5±1.4% / 89.4±1.7% and 97.9±0.7% / 95.2±1.2%, respectively. 4y / 8y EFS of the patients of 1 to 5 years old (n=300) and 6 to 9 years old (n=88) are 93.5±1.4% / 93.0±1.5% and 84.9±3.9% / 75.8±5.8%, respectively (log rank p=0.0003). 4y / 8y EFS of the patients with day 15 M1 marrow (n=287 ) was 92.8±1.6% / 91.6±1.8%, while those of the patients with day 15 M2 marrow (n=101) was 88.0±3.3% / 83.7±3.9% (log rank p=0.0446). When 388 patients were further classified into 4 subgroups based on genetic abnormalities, such as ETV6-RUNX1 (n=89, 22.9%), high hyperdiploid (HHD) (n=97, 25%), normal karyotype (n=147, 37.9%), and others (n=55, 14.2%), 4y-EFS/OS of each group was 97.6±5.9 /100% (ETV6-RUNX1), 91.5±2.9 /100% (HHD), 89.6±2.5 /95.1±1.8% (normal karyotype), and 86.9±4.6 /98.2±1.8% (others), suggesting poor EFS of B-others group. When HHD subgroup was divided into two groups, such as triple trisomy (TT; n=35) (trisomy of chromosome 4,10,17) and non-TT (n=62), 4y-EFS of each sub-group was 100% and 84.5±4.5%, respectively (log rank p=0.0161). Interestingly, day 15 M2 marrow was associated with poor 4y/8y EFS only in the normal karyotype subgroup (day 15 M1 vs M2 92.0±2.6% / 90.2±3.1% vs, 81.3±6.9% / 77.2±7.7%, log rank p=0.0497). The rates for NCI-CTC grade 4 infection, allergy, increase of transaminase were 1.80%, 0.26%, and 22.9%, respectively. Multivariate analysis identifies the patients of 6 to 9 years old (HR=3.178, p=<0.001) as a predictor of poor prognosis in EFS and day 15 M2 marrow (HR=3.273, p=0.027) and B-others subgroup (HR=11.1, p=0.0017) as predictors of poor prognosis in OS.

Discussion: Although JACLS ALL-02 SR protocol was less intensive chemotherapeutic regimen compared to the contemporary protocols used for NCI-SR patients, good outcome of the 4y EFS and OS (91.5±1.4 % and 97.9±0.7 %) was achieved with good feasibility. Because the specific genetic subgroups such as B-others and HHD without TT were associated with relatively poor outcome, those patients should be treated with more intensive chemotherapy, especially for the patients showing initial poor response (day 15 M2). On the other hand, ETV6-RNUX1 and TT subgroups showed excellent outcome. Thus, appropriate reduction of therapy should be explored for these subgroups.