Multiple myeloma (MM) is a hematological malignancy characterized by the proliferation of clonal malignant plasma cells in the bone marrow. While new treatment options have improved survival, the disease still carries a risk of recurrence and treatment resistance. This study aimed to evaluate the expression levels of miR-21, miR-32, miR-181a, and miR-181b in peripheral blood of MM patients before and after treatment, and to investigate the relationship between these miRNAs and clinical treatment response.

The study included 38 MM patients and 20 healthy controls. Clinical and laboratory characteristics of the patients were recorded. miR-21, miR-32, miR-181a, and miR-181b expression levels were measured before and after treatment using the SYBR Green-based real-time quantitative polymerase chain reaction method. Post-treatment changes in miRNA expression were compared with objective treatment response.

In MM patients, miR-32, miR-181a, and miR-181b expression levels were found to be 6.3, 2.7, and 4.1 fold higher, respectively, compared to the control group, and the differences were statistically significant (p < 0.0001, p = 0.002, and p < 0.0001, respectively). Although miR-21 expression was 1.9 fold higher in the MM group, this difference did not reach statistical significance (p = 0.08). After treatment, a significant decrease was observed in all miR-21, miR-32, miR-181a, and miR-181b expression levels compared to pre-treatment levels (p < 0.05). A decrease in miR-32 expression was observed more frequently in patients with an objective treatment response. In the age and sex-adjusted analysis, the decrease in miR-32 expression was significantly associated with objective treatment response (OR = 6.502; 95% CI: 1.154–36.636; p = 0.034). Changes in miR-21, miR-181a, and miR-181b did not reach statistical significance in relation to treatment response.

The increased expression of miR-32, miR-181a, and miR-181b in MM patients, and the decrease in all four miRNAs after treatment, suggest that these molecules may be related to disease biology and the biological response to treatment. In particular, the association of decreased miR-32 expression with objective treatment response indicates that miR-32 could be a candidate biomarker for monitoring treatment response. The significant post-treatment decrease in miR-21, miR-181a, and miR-181b levels suggests that these miRNAs could be candidate monitoring markers for MM; however, their lack of a significant association with objective treatment response indicates that their predictive value is limited. However, these findings need to be confirmed in larger and independent patient cohorts.