An extra chromosome 9 derived from either a normal chromosome 9 or a derivative chromosome 9 in a patient with acute myeloid leukemia positive for t(9;11)(p21.3;q23.3): A case report

Translocation (9;11)(p21.3;q23.3) is one of the most common lysine methyltransferase 2A (KMT2A)-rearrangements in de novo and therapy-related acute myeloid leukemia (AML). Numerous in vitro and in vivo studies have demonstrated that the KMT2A/MLLT3 super elongation complex subunit (MLLT3) fusion gene on the derivative chromosome 11 serves a crucial role in leukemogenesis. Trisomy 9 as a secondary chromosome change in patients with t(9;11) is relatively rare. The present study reported a unique case of AML with a chromosome 9 trisomy secondary to t(9;11)(p21.3;q23.3) through the cytogenetic analysis of leukemic blood and bone marrow. Further characterization with fluorescence in situ hybridization and array comparative genomic hybridization analysis revealed that this extra chromosome 9 was either a copy of normal chromosome 9 or a derivative chromosome 9. Conversely with the previously reported favorable outcome of AML patients with t(9;11)(p21.3;q23.3), in the present study, the cells with only translocation persisted, whereas the cells with an extra chromosome 9 disappeared following initial chemotherapy. With this unique case, the present study hypothesized that the extra chromosome 9 could serve a crucial role in AML disease progression and contribute to cellular sensitivity to chemotherapy.