Material and Method:
Our study included pediatric ALL patients treated with the modified St Jude Total Therapy XV (Total XV) protocol during January 2011- December 2018, aged 1-18 years, who were diagnosed, and completed all the treatment in our hospital and followed up without interrupting their follow-up. Patients who were younger than 12 months of age at the time of admission, biphenotypic feature, had previous diagnoses such as myelodysplastic syndrome and Fanconi aplastic anemia, had previously received chemotherapy for other reasons, relapsed ALL patients, patients who did not come for regular follow-ups, continued their treatment in other centers and the patients who came to our hospital from other centers were excluded from the study. Again, the study did not include patients with mature B-cell (Burkitt) leukemia with different treatment protocols.
For the diagnosis of ALL, bone marrow aspiration was performed to evaluate the morphological findings in the staining of slides with Giemsa. Also, a 10 mL sample was taken from the bone marrow into an ethylenediaminetetraacetic acid (EDTA) tube, and cell surface markers of the blastic population were studied with flow cytometry (BD FACSCanto, BD Biosciences USA). Blastic cell populations for over 25% with flow cytometry were also diagnosed as ALL.
To classify risk groups, FISH and PCR methods were used to analyses and evaluate t(9;22) (q34;q11.2); BCR_ABL, t(12;21) (p13;q22); TEL-AML1 (ETV6-RUNX1), t(1;19) (q23;p13.3); TCF3-PBX1, t(v;11q23) (MLL rearranged) regions and chromosome analysis was performed via karyotyping. Patients were classified initially into three risk groups according to St Jude’s Total XV protocol risk criteria based on patient age and leucocyte count at baseline and leukemic cell phenotype and genotype. The risk status of the patients was changed according to the level of minimal residual disease during and after remission induction therapy. Patients with 1% or higher minimal residual disease on day 19 of remission induction or between 0.01% and 0.99% on day 46 were included in the standard-risk ALL group. Patients with minimal residual disease of 1% or higher following completion of remission induction or 0.1% or higher on week 7 of maintenance treatment were included in the high-risk ALL group.
The patients were treated with the St Jude Children’s Research Hospital Total XV protocol [15] with a minor modification. (The only modification was methylprednisolone 20 mg/kg/day for 7 days, 10 mg/kg/day for the second 7 days, and 2 mg/kg/d for other days instead of prednisolone 40 mg/m2/day orally in the induction phase).[16]
The chemotherapy regimens of all risk groups are summarized in a supplementary file.
CNS prophylaxis consisted of triple intrathecal therapy (MTX, cytarabine, and prednisolone), irrespective of the CNS status and the risk group; the total doses administered were based on the CNS status and the risk classification and ranged from 13 to 25. The number of intrathecal therapy doses administered was 13 for LR cases and ranged from 16 to 25 for IR/HR cases. None of our patients had refractory CNS leukemia and did not require cranial irradiation.
During treatment, all patients were given trimethoprim-sulfamethoxazole for Pneumocystis jirovechii prophylaxis, while patients with invasive fungal infections were given voriconazole prophylaxis until the end of their treatment. International febrile neutropenia protocols were used during febrile neutropenia periods, and all patients during febrile neutropenia periods were hospitalized and given broad-spectrum antibiotics and, if necessary, antifungal and antiviral treatments.[17, 18]
If there is an eligible donor, stem cell transplantation was performed on patients in the HR group or those with MRD positivity at week 7 on continuation treatment.
MRD studies
Minimal residual disease levels were measured in bone marrow specimens by multiparameter flow cytometry on days 19 and 46 of remission induction and weeks 7, 17, 48, and 120 (end of treatment for girls) or 146 (end of treatment for boys) of maintenance treatment. The leukemia markers that were used to study minimal residual disease by multiparameter flow cytometry are listed in Table 2.
Data of patients were retrospectively collected using the medical records in the electronic file system (MEDIN HBYS, Erguvan Information Technologies, Turkey) for five years, and age, gender, risk group, cell type, course of the disease, and follow-up period were recorded electronically (Microsoft Office 2013 package program Excel, Microsoft USA). Statistical analysis was done with SPSS 20.0 package program (IBM USA).
After finishing their treatment plan, patients continued to follow-up evaluations in the pediatric hematology outpatient policlinic every month during the first 6 months, every other month for the second 6 months, every three months for the next two years, every 6 months for five years, and then annually thereafter.
As appropriate, comparisons between categorical variables were carried out using either the Pearson-X² test or Fisher exact test. The duration of event-free survival (EFS) was calculated from the first day of treatment to the time of analysis (September 2021) or to the first event (early death, relapse, or death during remission). EFS and overall survival (OS) rates were estimated using the Kaplan-Meier method, and the survival curve was arranged in the SPSS 20.0 for Windows (SPSS Inc., Chicago, IL). The Mantel-Cox (Log Rank) test was used to analyze the factors affecting mortality. A P-value <0.05 was considered statistically significant.
The study was approved by the institutional ethics committee, and written informed consent was obtained from parents or guardians at the beginning of treatment.