Expression and prognostic value of miR-26b-5p in Triple-Negative Breast Cancer (TNBC): Evidence from patient tissues and in silico analysis

Background: Triple-negative breast cancer (TNBC) is associated with a higher likelihood of early tumour relapse and reduced overall survival. MicroRNAs (miRNAs) are small non-coding RNA molecules that regulate gene expression by binding to target mRNAs, leading to transcript degradation or inhibition of translation. This study aimed to evaluate whether miR-26b-5p expression could serve as a prognostic biomarker for predicting recurrence risk and survival outcomes in TNBC. Methods: Total RNA was extracted from tumour and normal adjacent tissues of TNBC patients. The expression level of miR-26b-5p was quantified using RT-qPCR. Potential target genes of miR-26b-5p were identified and survival analysis was performed using METABRIC and TCGA TNBC patient cohorts. Results: The expression level of miR-26b-5p was significantly downregulated in tumour compared to normal adjacent tissues (-4.64 vs -2.29, p=0.001) of TNBC patients. Significant downregulation of miR-26b-5p was also observed in TNBC, which had positive axillary lymph nodes compared to negative axillary lymph node metastases (-2.80 vs -0.0454, p=0.049) as well as in TNBC patients who had disease recurrence compared to non-disease recurrence groups (-3.908 vs -1.536, p=0.009). Survival analysis demonstrated that high miR-26b expression was significantly associated with improved survival rate and high SMAD1 expression was correlated with an increased risk of relapse and poorer survival rates. Conclusion: miR-26b-5p is significantly downregulated in TNBC tumours, particularly in patients with lymph node metastasis and disease recurrence. Its low expression correlates with poorer survival, highlighting its potential as a prognostic biomarker for TNBC recurrence risk.