Expression Profiling of MicroRNAs in Breast Cancer Subtypes Among Nigerian Women at University College Hospital Ibadan

MicroRNAs (miRNAs) are small non-coding RNAs that regulate gene expression post-transcriptionally and play critical roles in cancer initiation, progression, and metastasis. Expression profiling of miRNAs in breast cancer subtypes reveals subtype-specific regulatory signatures with diagnostic and therapeutic potential. Breast cancer in Nigerian women is characterised by a high prevalence of the aggressive triple-negative subtype, necessitating subtype-specific miRNA studies. This study profiled miRNA expression across breast cancer subtypes (luminal A, luminal B, HER2-enriched, and triple-negative) in Nigerian patients at University College Hospital (UCH), Ibadan, Oyo State. Sixty freshly collected tumour biopsy specimens were obtained from histologically confirmed breast cancer cases. Total RNA including small RNA fractions was extracted and subjected to high-throughput miRNA sequencing on the Illumina HiSeq platform. Differentially expressed miRNAs were identified using DESeq2, with functional enrichment analysis using miRNet and Ingenuity Pathway Analysis. Triple-negative tumours exhibited significant upregulation of oncogenic miR-21 and miR-155, and downregulation of miR-200 family members involved in epithelial-mesenchymal transition suppression. Distinct miRNA signatures were identified for each subtype. Candidate miRNAs with diagnostic potential were validated by qRT-PCR in an independent validation cohort. Keywords: miRNA, breast cancer, triple-negative, expression profiling, Ibadan