Cryptic to conventional cytogenetics: Philadelphia-like ALL presenting with hypereosinophilia

BCR::ABL1-like B-lymphoblastic leukaemia (B-ALL) neoplasms lack the BCR::ABL1 translocation but have a gene expression profile like BCR::ABL1 positive B-ALL. This includes alterations in cytokine receptors and signalling genes, such as CRLF2, ABL1, ABL2, JAK2, PDGFRB and EPOR. Cases with CRLF2 rearrangements account for approximately 50% of cases of Philadelphia-like acute lymphoblastic leukaemia (Ph-like ALL), and the frequency of specific genomic lesions varies with ethnicity such that IGH::CRLF2 translocations are more common in Hispanics and Native Americans. We report two cases of BCR::ABL1-like ALL, with significant eosinophilia. A Hispanic man in his early 20s and a Hispanic woman in her 50s presented with leukocytosis and eosinophilia. Bone marrow flow cytometry revealed lymphoblasts expressing CD19, CD10, partial CD20, CD22, CD79a, CD38, CD34, TdT and HLA-DR. Examination of the bone marrow biopsy and aspirate exhibited a hypercellular bone marrow with increased blasts and elevated eosinophils. Fluorescence in situ hybridisation (FISH) demonstrated a cryptic chromosomal rearrangement between the X chromosome and chromosome 14 at breakpoints involving IGH at 14q32 and CRLF2 at Xp22.33, t(X;14)(p22.33; q32). These findings confirmed the diagnosis of BCR::ABL1-like B-ALL with IGH::CRLF2 rearrangement. One patient (man) attained complete remission with induction therapy using the paediatric CALGB 10403 protocol, while the other patient (woman) had a poor outcome after receiving a hyper-fractionated cyclophosphamide, vincristine, doxorubicin and dexamethasone regimen. These two cases demonstrate an unusual presentation of BCR::ABL1-like B-ALL and emphasise the importance of appropriate cytogenetic studies for correct diagnosis. When treated with conventional chemotherapy, these cases carry a poor prognosis and might require allogeneic transplantation.