[Screening of MLL fusion genes and rare breakpoint cases in patients with acute myeloid leukemia].

<b>Objective:</b> To screen for patients with mixed-lineage leukemia (MLL) fusion gene-positive with acute myeloid leukemia (AML), analyze the clinical characteristics and prognosis of patients with AML with positive fusion genes, and report two cases with rare breakpoint sites. <b>Methods:</b> This study included 287 patients with AML (non-acute promyelocytic leukemia) admitted to the Hematology and Oncology Research Center of Harbin First Hospital from October 2021 to October 2023. The cohort involved 157 males and 130 females, with a median age of 48 years (range: 19-80 years). All 287 patients underwent screening for 56 fusion genes and chromosome karyotyping analysis. Fluorescence in situ hybridization (FISH) and RNA seq were further performed on patients with negative fusion genes but positive 11q23.3 chromosomal translocation. Patient observation indicators included remission, recurrence, and others. <b>Results:</b> Among the 287 patients with AML, 15 were positive for the MLL fusion gene, with a positivity rate of 5.2%. Among the 11 types of MLL fusion genes detected, the most prevalent fusion types were MLL-ENL (4 cases), MLL-ELL (4 cases), MLL-AF9 (3 cases), and MLL-AF6 (3 cases). Of the 15 patients with positive MLL fusion gene, 2 demonstrated negative fusion gene while exhibiting positive chromosome and FISH. RNA-seq testing in these two patients revealed an uncommon breakpoint in the MLL fusion gene and a novel breakpoint fusion site, respectively. Complete remission (CR) was achieved in 6 patients with positive MLL fusion genes during the first chemotherapy cycle. After two cycles, eight patients achieved CR, with 50% of them experiencing recurrence within 2 months. <b>Conclusion:</b> RNA seq technology is useful for screening fusion genes with unconventional or novel cleavage sites, and patients with positive MLL fusion genes demonstrated a poorer prognosis.