3.1 Baseline characteristics of patients
Totally, 1,668 eligible pediatric patients were enrolled in this study. The baseline characteristics of the eligible patients were presented in Table 1. Of them, 993 (59.5%) are male and 675 (40.5%) are female with a median age of 7.6 years old. According to the immunophenotype, 721 (43.2%) patients were diagnosed as B-precursor ALL.In addtion, Fusion gene was detected in 1,307 patients via conventional G-banding analysis and the most common positive fusion gene was ETV6/RUNX1. Among the pediatric patients, the median of initial WBC was 33.7×109/L (range 0.4-1306.0×109/L), and the median DI was 1.0 (range 0.0-1.9).
As a result, 222 patients accept 9906 protocol, 789 patients accept AALL0232, 415 patients received AALL0331 protocol and the remaining 242 patients received AALL0434 protocol. As for the early treatment response, 1,154 patients responded well to prednisone on Day+8, while the remaining 514 patients did not respond well to prednisone. Most of the pediatric patients (n=1,625) achieved CR at the end of remission induction chemotherapy (Day +29).
The median follow-up for those patients was 7.7 years (range 0.1-15.7 years). Finally, 309 patients subsequently developed hematological relapse (presence of leukemic blasts > 5% in BM), 113 patients developed CNS relapse and testes site of relapse occurred in 11 children.The probability of 10-year EFS and OS were reported to be 68.3 ± 2% and 79.6 ± 2%, respectively (Fig 1).
3.2 Early treatment response
We conducted a univariate and multivariate analysis of the early treatment response on Day +29 after induction chemotherapy among childhood ALL. Factors associated with a significantly elevated of early treatment response from univariate analysis were: age,WBC, immunophenotype, karyotype, fusion gene, prednisone response and chemotherapy protocol (Table 2). No association early treatment response was found with the gender, race, DI and CNS status. Results from the multiple regression analysis found that age≥10 years(OR=9.7, 95%CI 1.6-59.1,P=0.014), B Cell ALL(OR=0.2, 95%CI 0-0.7, P=0.019), B precursor (Non-T, Non-B)(OR=0.1, 95%CI 0-0.8, P=0.034), hyperdiploid(OR=0.2, 95%CI 0-0.6, P=0.009), BCR/ABL1 fusion gene(OR=7.6, 95%CI 2.4-24.3, P<0.001), poor prednisone response (OR=16.9, 95%CI 6.3-45.9, P<0.001), AALL0232 protocol (OR=0, 95%CI 0-0.5, P=0.011) and AALL0434 (OR=0, 95%CI 0-0.1, P<0.001) protocol were the independent risk factors (Table 2).
3.3 Multivariate analysis of prognostic factors
When we included DI with other risk factors in the Cox model, including age, gender, race, WBC, fusion gene, prednisone response, BM blasts Day+29, immunophenotype and karyotype as co-variables, we identified DI as an independent factor for both EFS and OS
in pediatric patients with ALL (Table 3). DI was significantly associated with better EFS (HR=0.9, 95%CI 0.3–2.0, P= 0.048) and OS (HR=0.1, 95%CI 0–0.5, P= 0.001). Those patients with ETV6/RUNX1 fusion gene were also significantly associated with better EFS (HR=0.6, 95% CI 0.4–0.8, P= 0.003) and OS (HR=0.3, 95%CI 0.2–0.5, P<0.001) compared to patients with no
ETV6/RUNX1. On the contrary, BM NR on Day+29 showed a significant decrease in EFS (HR=3.1, 95%CI 2.1–4.5, P<0.001) and OS (HR=1.7, 95%CI 1.1–2.8, P=0.026).
3.4 The value of DI cut-point among prognostic impact of pediatric ALL
Generalized additive models(Fig 2) was used to visually assess functional relationships between DI and the risk of adverse clinical outcomes. This analysis was conducted using both logarithmic transformed and untransformed data. Log (relative risk) can be converted to a relative risk by taking antilog. For example, a log (relative risk) of 0 implies the relative risk of 1 (no impact on the probability of having adverse clinical outcomes), whereas a log (relative risk) of 1 implies the relative risk of 2.71 (ie, 2.71-fold increase in the probability of having adverse clinical outcomes). After adjusting for these possible factors related to adverse clinical outcomes, including gender, age, race, chemotherapy protocol, WBC, CNS status, fusion gene, prednisone response, BM blasts day+29, immunophenotype and karyotype, the U-shaped relationships between DI and adverse clinical outcomes were confirmed in multivariable analyses. The threshold effect of DI on poor outcome was significant after adjusting for potential confounders. The adjusted regression coefficient (Log RR) was 0.7 (95%CI 0.1-3.2, P=0.597) for DI <1.1 while 8.8 (95%CI 1.4-56.0, P=0.021) for DI≥1.2 and 0.0 (95%CI 0.0-0.8, P=0.041) for 1.1≤DI<1.2 (Table 4). Analyses showed that the lowest rates of the adverse outcomes estimated to occur among DI between 1.1 and 1.2. Moreover, a poor outcome significantly increased with increasing DI after the turning point (DI≥1.2)(Fig 2).
3.5 Survival analysis of DI cut-point
Base on DI cut-point of 1.1 and 1.2 obtained above, we analyzed the survival as just three groups having different DI ranges ( DI<1.1, 1.1≤DI<1.2 and DI≥1.2). As a result, the EFS of pediatric ALL with a DI between 1.1-1.2 were higher than those with DI of <1.1 or ≥1.2 (10-year EFS, 72.6±6% versus 67.7±2%, P=0.15), but no significant difference was found. However, the OS of pediatric ALL with a DI between 1.1-1.2 were significantly higher than those with DI of <1.1 or ≥1.2 (10-year OS, 88.9±4% versus 78.3±3%, P<0.05)(Fig 3, Fig 4).