This study investigates the role of microRNAs (miRNAs) in human breast cancer. The authors used microarray and Northern blot analyses to compare miRNA expression in normal breast tissues and breast cancer tissues. They found that miRNA expression patterns could clearly distinguish normal from cancer tissues, with mir-125b, mir-145, mir-21, and mir-155 being the most significantly deregulated. These miRNAs were also correlated with specific biopathologic features of breast cancer, such as estrogen and progesterone receptor expression, tumor stage, vascular invasion, and proliferation index. The study suggests that miRNA expression deregulation is a significant factor in the development and progression of breast cancer.This study investigates the role of microRNAs (miRNAs) in human breast cancer. The authors used microarray and Northern blot analyses to compare miRNA expression in normal breast tissues and breast cancer tissues. They found that miRNA expression patterns could clearly distinguish normal from cancer tissues, with mir-125b, mir-145, mir-21, and mir-155 being the most significantly deregulated. These miRNAs were also correlated with specific biopathologic features of breast cancer, such as estrogen and progesterone receptor expression, tumor stage, vascular invasion, and proliferation index. The study suggests that miRNA expression deregulation is a significant factor in the development and progression of breast cancer.