Introduction. Cytogenetic studies play an important role in determining the prognosis of acute lymphoblastic (ALL) and acute myeloid leukemias (AML), which affects the choice of treatment strategy. However, the division into groups of cytogenetic prognosis may lose its importance due to the lack of response to chemotherapy (CT) and the development of relapses. Today, the effectiveness of treatment of patients with relapses and refractory forms of ALL and AML remains insufficient.

The aim of the study was to determine the cytogenetic features of the mechanisms of formation of abnormal clones in the recurrence of ALL and AML.

Materials and methods. Cytogenetic studies were carried out in bone marrow (BM) cells of 31 patients in relapses of acute leukemia, among whom 22 were diagnosed with ALL and 9 with AML, received in the laboratory during 2012-2021. Preparations of metaphase chromosomes were prepared according to a generally accepted method and stained with G-bands. At least 20 metaphase plates were analyzed for each patient.

Results. A significant percentage of mosaic karyotypes was noted in relapses of ALL, which totaled 77.3%, among which A/4n/H dominated (55.6%). Trisomies of chromosomes led to the formation of hyperdiploid clones. Among additional chromosome abnormalities, trisomies of chromosomes 6, 21, and 5 were most often encounted. Most often, additional marker chromosomes were registered (31.8%). Chromosome trisomies were single in AML relapses. According to the mechanisms of formation of abnormal clones in relapses of GLL, structural abnormalities of chromosomes were recorded, among which balanced (translocations, inversions) and unbalanced (deletions, isochromosomes, additional material of unknown origin, duplications) were determined. Losses of genetic material (deletions) (34.2%) and translocations (39.5%) were detected more often. The total number of cases with translocation t(9;22)(q34;q11.2) is 21.1%. Chromosomes 1, 3, 5, 6, 12, 14, 15, 17, 19, 21, 22 and sex chromosome X were involved in structural rearrangements.

In relapses of AML, among structural abnormalities, deletions and translocations were more often detected (41.7% each). Chromosomes 5, 7, 8, 9, 11, 12, 16, and 22 were involved in the structural rearrangements. 95.4% of karyotypes were assigned to the group of unfavorable cytogenetic prognosis in ALL, 55.6% in AML.

Conclusions. In ALL, abnormal karyotypes were formed due to quantitative (trisomies, monosomies, marker chromosomes) and structural abnormalities of chromosomes, more often they were translocations (39.5%) and deletions (34.2%). In AML, deletions and translocations were more often registered (41.7% each). In ALL, marker chromosomes (31.8%) and t(9;22)(q34;q11.2) (21.1%) were recorded. In ALL, 95.4% of karyotypes belong to the unfavorable prognosis group, in AML – 55.6%. The presence of the evolution of chromosome abnormalities and independent clones both in relapse and at diagnosis in ALL and AML may indicate the formation of resistance to CT.

Keywords: acute leukemias, relapses, quantitative and structural chromosome abnormalities.