Let-7 directly targets KRAS mRNA in a variety of tumors including lung and breast cancer.45However, surprisingly, an analysis showed that Let-7 provided increased expression in metastatic CRC tissues compared with normal mucosa, but only in KRAS-mutated tumors.46Researchers concluded that this microRNA could be applied as a distinctive biomarker regarding treatment with anti-EGFR targeted therapy like cetuximab. This evidence concerns the gene KRAS and breast cancer.