MOLECULAR CHARACTERIZATION OF DIFFERENT GENE FUSIONS ASSOCIATED WITH ACUTE LYMPHOBLASTIC LEUKEMIA IN CHILDREN FROM THE BRAZILIAN AMAZON

Abstract

Objective: Acute Lymphoblastic Leukemia (ALL) is classified according to its genetic abnormalities, which are associated with the clinical and biological characteristics of the disease. The detection of gene fusions assists in diagnosis, risk stratification, and targeted therapy. This study aims to evaluate the status of gene fusions in pediatric ALL patients from the Brazilian Amazon and their association with known hematological parameters. Materials and methods: The research was approved by the ethics committee under number 4.040.805 and included a total of 160 patients diagnosed with ALL at the Octávio Lobo Children's Oncology Hospital during the period from 2017 to 2023. Clinical data (leukometry, platelets, and hemoglobin) and epidemiological data (gender and age) were collected from the hospital's database system. For the analysis of gene fusions, c-DNA was obtained for the detection of molecular biomarkers by PCR using specific primers. Agarose gel electrophoresis was performed to visualize the PCR products. Finally, Sanger Sequencing was carried out to confirm the PCR results. For qualitative variables, descriptive statistics were used, determining absolute and percentage frequencies. For quantitative variables, median and standard deviation values were calculated according to the variables under study. The Kruskal-Wallis test was performed to test the association of the presence of one of the gene fusions (BCR::ABL, TCF3::PBX1, KMT2A::AFF1, ETV6::RUNX1 and SIL::TAL) with the clinical data, adopting a p-value ≤ 0.05 as significant. Statistical analyses were performed using RStudio 12.1 software. Results: Regarding gene fusions, 21% of patients had the TCF3::PBX1 fusion, 19% ETV6::RUNX1, 11% BCR::ABL, 3% KMT2A::AFF1, 2% SIL::TAL, and 44% had none of the studied fusions. 61% of the patients were male and 39% female, with a median age of 6 years. Regarding clinical data, the patients had a median white blood cell (WBC) count of 13,150/mm3; a median platelet count of 36,000/mm3; and a median hemoglobin level of 8 g/dL. The Kruskal-Wallis test revealed a significant statistical difference between gene fusions and white blood cell count (p-value = 0.0024), and Dunn's post-test showed that in TCF3::PBX1, the WBC count is significantly higher mainly compared to ETV6::RUNX1 (p-value = 0.007). Discussion: Studies have reported ETV6::RUNX1 as the most frequent fusion, but this work found TCF3::PBX1 as the most frequent find, which may be explained by the highly mixed population of the Amazon, supporting the existence of ethnic differences. Other studies found significant statistical differences in white blood cell count between the TCF3::PBX1 fusion and others, which corroborates the findings of this study, indicating that this molecular biomarker has a poor prognosis and is characterized by a white blood cell count above 50,000/mm3, which was found in about 35% of the patients in this study. Conclusion: In the study, the frequency of the TCF3::PBX1 fusion was observed to be relatively higher than what is reported in the literature. The TCF3::PBX1 fusion leads to the activation of genes encoding proteins with malignant potential, and that the fusion showed a statistical difference between groups regarding white blood cell count, which is used as a risk classification according to the National Cancer Institute.