<h4>Background</h4>Genetic variations in tumor suppressor miRNAs and the 3'UTR of their target genes influence tumor biology and breast cancer (BC) risk.<h4>Objective</h4>This study investigated genetic variations in tumor suppressor miRNAs (hsa-let-7c, hsa-miR-34a, hsa-miR-145a) and their target genes (KRAS, IGFBP6, IGF1R), and their functional significance in BC patients.<h4>Methods</h4>The miRNA encoding regions and 3'UTRs of the selected target genes were sequenced in 208 BC patients. This evidence concerns the gene KRAS and breast carcinoma.