Objective:To investigate the levels and clinical significances of miRNA-155-5p (miR-155-5p) and hypoxia inducible factor-1α (HIF-1α) in the bone marrow of patients with acute myeloid leukemia (AML)-M 5. Methods:A cross sectional study was conducted. The bone marrow samples were collected from 32 AML-M 5 patients who were admitted to the First Affiliated Hospital of Hebei North University from November 2023 to December 2024, and the bone marrow samples collected from 11 patients with megaloblastic anemia from November 2023 to May 2025 were used as controls. Reverse transcription real-time fluorescence quantitative polymerase chain reaction (qRT-PCR) was used to determine relative expression of miR-155-5p at the transcription level in bone marrow mononuclear cells, and enzyme-linked immunosorbent assay (ELISA) was used to measure the concentration of HIF-1α protein in bone marrow supernatant. The levels of miR-155-5p and HIF-1α in bone marrow were compared between AML patients and control group, as well as among AML patients with different prognostic risks. Spearman method was used to analyze the relationship between miR-155-5p level and HIF-1α level in bone marrow of AML patients and their levels with bone marrow and peripheral blood cell indicators. Results:Among the 32 AML-M 5 patients, 20 patients (62.5%) were male and 12 patients (37.5%) were female, with a median age [ M ( Q1, Q3)] of 63 (51, 70) years; according to the clinical response criteria recommended by the European Leukemia Network (ELN) in 2022, there were 12 cases (37.5%) of complete response (CR) and 8 cases (25.0%) of non-complete response (NCR); according to the risk stratification criteria recommended by ELN in 2022, there were 8 cases (25.0%) with good prognosis, 13 cases (40.6%) with moderate prognosis and 11 cases (34.4%) with poor prognosis. In the control group, there were 5 males and 6 females, with a median age of 68 (63, 72) years. There was no statistically significant difference in gender and age between the two groups (both P > 0.05). The transcription level relative expression of miR-155-5p in the bone marrow mononuclear cells of AML-M 5 patients [5.13 (2.83, 8.84) vs. 0.87 (0.56, 1.69)] and the concentration of HIF-1α protein in the bone marrow supernatant of AML-M 5 patients [(116±32) pg/ml vs. (58±22) pg/ml] were higher than those in the control group, and the differences were statistically significant (both P < 0.001). The relative expression of miR-155-5p at the transcription level in the initial diagnosis group and NCR group and the concentration of HIF-1α in the initial diagnosis group, NCR group and CR group were higher than those in the control group (all P < 0.01), the relative expression of miR-155-5p at the transcription level in the CR group was higher than that in the control group, but the difference was not statistically significant ( P > 0.05); the relative expression of miR-155-5p at the transcription level in the newly diagnosis group was higher than that in the CR group, and the difference was statistically significant ( P < 0.01). However, there was no statistically significant difference between the newly diagnosis group and the NCR group or between the NCR group and the CR group (all P > 0.05). The concentration of HIF-1α in the newly diagnosis group and NCR group was higher than that in the CR group, and the differences were statistically significant (both P < 0.05). However, there was no statistically significant difference between the newly diagnosis group and the NCR group ( P > 0.05). There was no statistically significant difference in the relative expression of miR-155-5p at the transcription level and HIF-1α concentration in bone marrow among AML-M 5 patients with poor prognosis, moderate prognosis and good prognosis (both P > 0.05). The level of miR-155-5p in the bone marrow of AML-M 5 patients was positively correlated with the level of HIF-1α ( r = 0.446, P = 0.010); the level of miR-155-5p in bone marrow was positively correlated with the proportion of bone marrow primitive cells ( r = 0.583, P < 0.001), peripheral blood leukocyte count ( r = 0.464, P = 0.008), peripheral blood monocyte count ( r = 0.464, P = 0.007), and peripheral blood monocyte-to-leukocyte ratio ( r = 0.457, P = 0.009). The concentration of HIF-1α in the bone marrow of AML-M 5 patients was positively correlated with the proportion of bone marrow primitive cells ( r = 0.568, P = 0.001) and peripheral blood mononuclear cells-to-white blood cells ratio ( r = 0.375, P = 0.034), but not with peripheral blood white blood cell count ( r = 0.159, P = 0.385) or peripheral blood mononuclear cell count ( r = 0.300, P = 0.095). Conclusions:The levels of miR-155-5p and HIF-1α in the bone marrow of AML-M 5 patients are relatively high, and the levels of both are lower in patients with remission. However, the levels of both may not be related to the risk of prognosis. The levels of miR-155-5p and HIF-1α in the bone marrow of AML-M 5 patients are positively correlated, and their levels are also positively correlated with major hematological indicators in the bone marrow and peripheral blood.