Micro ribonucleic acid-21 expression and its association with resistance to neoadjuvant chemotherapy in breast cancer: preliminary results

Abstract

Objective: To evaluate the expression of micro ribonucleic acid (miR)-21 in the plasma of breast cancer patients and
investigate its potential association with resistance to neoadjuvant chemotherapy. Methods: All breast cancer patients
with an indication of neoadjuvant chemotherapy and submitted to surgical treatment at the Breast Unit of Hospital de
Clinicas de Porto Alegre, Rio Grande do Sul, Brazil, between 2023 and 2024 were selected. Chemotherapy resistance was
determined through clinical outcomes (e.g., pathological complete response vs. residual disease). Patients were grouped
based on their pathological response to chemotherapy: complete response, partial response, or no response. The miR-21
was isolated from patients’ plasma collected before chemotherapy. The expression of miR-21 was quantified by quantitative
reverse transcription polymerase chain reaction (qRT-PCR). Assessment of the association between miR-21 expression and
chemotherapy response was performed with the Student’s t-test or analysis of variance (ANOVA). Tumors were classified
into high- and low-expressing tumors, based on the median miR-21 expression values. Statistical analysis was performed
using IBM Statistical Package for Social Sciences (SPSS), version 18. Results: Patients with elevated plasma miR-21 levels
were significantly more likely to belong to the no-response group, accounting for 70% of the non-responders. In contrast,
lower miR-21 levels were associated with a 2.6 times higher probability of partial response (p<0.001). Conclusion: Our
preliminary results suggest that miR-21 expression in plasma could serve as a potential biomarker for predicting resistance to neoadjuvant chemotherapy in early breast cancer patients. Further studies are needed to validate these findings
and explore the role of miR-21 in chemotherapy resistance.