Background: Breast cancer initiation is an unresolved phenomenon although many genes are known to be involved in its initiation but its exact etiology is still unexplained in many aspects and recently microRNAs are found to regulate many genes expressions. Method: This case control study has been designed to evaluate the role of selected miRNAs in gene expression and subsequent association with drug resistance. Genetic polymorphisms were confirmed by PCR-SSCP followed by sequencing and microRNA expression was measured by realtime PCR with specific primers. Follow up was done for patients whose samples were used in the study. Results: This study revealed 15 germline mutations in mdr1, 5 in ABCG2, 8 in BRCA1 and 8 in PTEN gene. These mutations were significantly associated with breast cancer compared with control tissues (P<0.05). miR-21, miR-146a and miR-328 were over expressed whereas miR-451 was under expressed. Progression free survival (PFS) was linked with reduced polymorphisms in genes as well as microRNAs. Conclusion: Over expression of miRNA-21 and miRNA-146a may lead towards lower expression of PTEN and BRCA1 genes causing cancer progression. miRNA-328 and miRNA-451 reduced expression resulted in overexpressed ABCG2 and MDR1 genes in this study.
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