MicroRNAs (miRNAs) are small noncoding RNAs that regulate gene expression by targeting mRNAs, leading to translation repression or RNA degradation. Aberrant miRNA expression has been linked to various diseases, including cancer. This study investigates miRNA expression in human breast cancer and normal breast tissue. miRNAs were found to be aberrantly expressed in breast cancer, with mir-125b, mir-145, mir-21, and mir-155 showing the most significant deregulation. These miRNAs were confirmed by microarray and Northern blot analyses. The study identified miRNAs correlated with specific breast cancer features, such as hormone receptor expression, tumor stage, vascular invasion, and proliferation index. The study used miRNA microarrays to profile miRNA expression in 10 normal and 76 tumor breast tissues. ANOVA and class prediction tools were used to identify differentially expressed miRNAs. A cluster analysis showed clear separation between normal and cancer tissues based on miRNA expression. The results were validated by Northern blot analysis of mir-125b, mir-145, and mir-21, confirming their deregulation in breast cancer. The study also analyzed the biological functions of miRNAs by predicting their targets. miR-10b, miR-125b, miR-145, miR-21, and miR-155 were found to be the most consistently deregulated miRNAs in breast cancer. These miRNAs may act as tumor suppressor or oncogene genes. The study found that miR-125b is down-regulated in breast cancer, suggesting its role in cell differentiation. The results indicate that miRNA deregulation is involved in human breast cancer pathogenesis. The study highlights the importance of miRNA in cancer development and progression. It suggests that miRNA expression profiling could be a valuable tool for understanding the molecular basis of breast cancer and identifying potential therapeutic targets. The findings contribute to the understanding of miRNA's role in cancer and support the idea that miRNA deregulation is a key factor in breast cancer development.MicroRNAs (miRNAs) are small noncoding RNAs that regulate gene expression by targeting mRNAs, leading to translation repression or RNA degradation. Aberrant miRNA expression has been linked to various diseases, including cancer. This study investigates miRNA expression in human breast cancer and normal breast tissue. miRNAs were found to be aberrantly expressed in breast cancer, with mir-125b, mir-145, mir-21, and mir-155 showing the most significant deregulation. These miRNAs were confirmed by microarray and Northern blot analyses. The study identified miRNAs correlated with specific breast cancer features, such as hormone receptor expression, tumor stage, vascular invasion, and proliferation index. The study used miRNA microarrays to profile miRNA expression in 10 normal and 76 tumor breast tissues. ANOVA and class prediction tools were used to identify differentially expressed miRNAs. A cluster analysis showed clear separation between normal and cancer tissues based on miRNA expression. The results were validated by Northern blot analysis of mir-125b, mir-145, and mir-21, confirming their deregulation in breast cancer. The study also analyzed the biological functions of miRNAs by predicting their targets. miR-10b, miR-125b, miR-145, miR-21, and miR-155 were found to be the most consistently deregulated miRNAs in breast cancer. These miRNAs may act as tumor suppressor or oncogene genes. The study found that miR-125b is down-regulated in breast cancer, suggesting its role in cell differentiation. The results indicate that miRNA deregulation is involved in human breast cancer pathogenesis. The study highlights the importance of miRNA in cancer development and progression. It suggests that miRNA expression profiling could be a valuable tool for understanding the molecular basis of breast cancer and identifying potential therapeutic targets. The findings contribute to the understanding of miRNA's role in cancer and support the idea that miRNA deregulation is a key factor in breast cancer development.