A new translocation partner for CBFB in acute myeloid leukemia, t(10;16)(p13;q22)

ABSTRACT

Cytogenetic abnormalities involving chromosome 16 are found in 5– 8% of acute myeloid leukemia (AML). These are typically a pericentric inversion inv(16)(p13.1q22) or a translocation, t(16;16)(p13.1;q22), involving the MYH11 and CBFB genes localized to chromosome 16p13.1 and 16q22, respectively. In addition, less common rearrangements include deletion of the long arm of chromosome 16, del(16) (q22), and cryptic insertions involving the MYH11 and the CBFB genes with otherwise normal karyotypes. In this report, we present the first AML case with a new translocation involving the CBFB gene. The more common CBFB - MYH11 fusion product resulting from the inversion and/or translocation of chromosome(s) 16 leads to an AML with monocytic and granulocytic differentiation and abnormal eosinophil component with large, purple to violet color eosinophilic granules. This entity typically corresponds to the adult AML-M4Eo in French-American- British (FAB) Classification and now called AML with inv(16)(p13.1q22) or t(16;16)(p13.1;q22);CBFB-MYH1 in the new 2017 WHO Classification. Patients may present with myeloid sarcoma at initial diagnosis or at relapse. We present a case of an 80-year-old male with a history of prostate cancer post radiotherapy who was referred for COVID-19 testing. A complete blood count with differential revealed neutropenia and a macrocytic anemia. A bone marrow biopsy and a bone marrow aspirate confirmed a diagnosis of AML with 33% blasts including myeloblasts and promonocytes. Interphase fluorescence in situ hybridization (FISH) analysis with a break-apart probe for CBFB showed an abnormal hybridization pattern consistent with rearrangement of CBFB in 66% of nuclei. Chromosome analysis revealed an abnormal karyotype with two related clones 47,XY, t(10;16)(p13;q22),+22[4]/48,idem,+8[16]. Sequential GTG-FISH confirmed that the 3’ region of CBFB was translocated to 10p13 in the t(10;16) and the 5’ region remained on 16q. Based on the karyotype, the patient’s bone barrow exhibits clonal evolution having acquired additional chromosome abnormalities (trisomy 22 and trisomy 8). Molecular studies by next generation sequencing showed NRAS p.Gln61Lys mutation with a VAF of 11.21%. No genomic alterations were detected in KIT, KRAS or FLT3 genes. AML with inv(16)(p13.1q22) or t(16;16)(p13.1;q22) is associated with a high rate of complete remission and favorable overall survival when treated with intensive consolidation therapy. However, their prognostic advantage may be affected by additional cytogenetic abnormalities and/or other gene mutations. Specifically, trisomy 22, is a frequent abnormality additional to inv(16) detected as a secondary finding which has been associated with an improved outcome when compared to the prognosis associated with inv(16) alone. Furthermore, KIT (in 30–40%), FLT3 (in 14%), NRAS (in 45%) and KRAS (in 13%) mutations are common in this AML type. The prognostic implications of KIT mutation (especially involving exon 8) do not appear to be significantly poor prognostic compared to other AML types. On the other hand FLT3-TKD mutations and trisomy 8 are associated with a worse outcome. The patient is currently receiving Vidaza 75 mg/m2, days 1–7 of a 28 days cycle with Venetoclax mg daily of a 28-day cycle and his clinical prognosis is currently unclear. Further analysis by DNA sequencing may help to characterize the molecular nature of the fusion gene product resulting from the novel t(10;16)(p13;q22). To the best of our knowledge, this is the first reported case of an AML patient with translocation t(10;16)(p13;q22) involving the CBFB gene. Given the rarity and lack of additional information regarding the effects of this abnormality, the prognosis and survival cannot be predicted.