<p>Neocentromeres are newly formed chromosomal regions that can replace the function of traditional centromeres and are well documented in human clinical studies. However, their occurrence in neoplasia, including acute leukemia, appears to be rare. We analyzed complex karyotypes in bone marrow cells from 113 patients with acute myeloid leukemia and one patient with acute lymphoblastic leukemia using centromeric/multicentromeric fluorescence in situ hybridization and identified four cases (3.5%) with derivative chromosomes exhibiting newly formed constrictions. Three of these patients had secondary leukemia following preexisting hematological disorders, suggesting a potential role for neocentromeres in disease progression. In all four cases, neocentromeres were detected on derivative chromosome 11. To our knowledge, this is the first report of neocentromeres derived from this chromosome in acute leukemia. All four patients in our study died; however, all exhibited complex karyotypes, which are independently associated with poor prognosis and an aggressive disease course. Neocentromeres are a rare but potentially important source of genomic instability in malignant diseases. Generally, the formation of a new constriction allows mitotic rescue of acentric chromosomes, preventing their loss. An increase in genomic alterations in tumor cells predicts a more aggressive disease course and adverse outcomes. Due to limited data, the prognostic significance of neocentromeres remains unclear. Further rigorous investigation is required to deepen our understanding of the mechanisms underlying neocentromere formation and their implications in cancer.</p>