CHARACTERIZATION OF THE PHILADELPHIA-LIKE SUBTYPE OF B-CELL ACUTE LYMPHOBLASTIC LEUKEMIA

Abstract

Introduction and objectives: B-cell precursor acute lymphoblastic leukemia (B-ALL) is characterized by a variety of genomic alterations relevant for risk stratification and prognosis of patients. Notably, Philadelphia-like (Ph-like) ALL is defined by a gene expression profile similar to Philadelphia-positive patients but without the historically known BCR::ABL1 rearrangement. The Ph-like subgroup is associated with an unfavorable prognosis and is observed in 15% of children and 40% of adolescents and young adults (AYA) with B-ALL. The characterization of this subgroup involves the evaluation of gene expression of 8 genes, and it is a complex challenge for centers of leukemia diagnosis. Given this scenario, the aim of this study is to establish a predictive genetic panel for defining the Ph-like subgroup in the Brazilian Unified Health System (SUS), thereby improving and expediting its diagnosis. Materials and methods: 108 samples from children and adult patients diagnosed with B-ALL according to World Health Organization criteria, and collected from different cancer treatment centers in Brazil were included. The patients were classified as B-other based on the absence of recurrent primary alterations: high-hyperdiploidy, ETV6::RUNX1, BCR::ABL1, TCF3::PBX1 and KMT2Ar. The Ph-like subgroup was characterized using cDNA samples to analyze the expression profile of SPATS2L, MUC4, CRLF2, CA6, NRXN3, BMPR1B, JCHAIN, and ADGFR1 genes by quantitative PCR (qPCR) using commercial TaqMan assays (Life Technologies). Gene expression profiles were correlated with the presence of rearrangements in genes frequently altered in this subgroup, including PDGFRB, CRLF2, JAK2, ABL1, ABL2, IGH and CSF1R, evaluated by Fluorescent in situ Hybridization (FISH) using break-apart probes (Zytovision and Cytocell). Patients positive for primary alterations were used as a reference control group. This study was approved by the Research Ethics Committee of INCA (CAEE #87793418.0.0000.5274). Results and conclusion: A total of 53 samples were included so far. Among them, 32 patients were classified as B-other and the remaining 21 patients had recurrent abnormalities: ETV6::RUNX1 (n = 6), BCR::ABL1 (n = 5), KMT2A-r (n = 3), TCF3::PBX1 (n = 3), and high-hyperdiploidy (n = 4). The Ph-like profile was identified in 37.5% of patients, based on the occurrence of CRLF2, ABL1 or JAK2 rearrangements and the expression profile, simultaneously. Most Ph-like patients were AYA (66.7%) and had low white blood cell count at diagnosis. It was observed that 11 of the 12 Ph-like patients had at least one overexpressed gene. Our preliminary results confirm the existence of distinct molecular profiles previously described among the subtypes of Ph+ and Ph-like B-ALL. While FISH has demonstrated effectiveness to identifying Ph-like cases when a differential gene expression was not observed, the current sample size is not enough to confirm the most appropriate diagnostic strategy for characterize this complex B-ALL subtype. Support: CNPq, FAPERJ, Ministério da Saúde, Swiss Bridge Foundation.