The KRAS gene encodes a small GTPase that plays a central role in transducing signals from the epidermal growth factor receptor (EGFR) to downstream effectors. KRAS protein transduces signals from membrane-bound receptors via multiple downstream effector pathways and thereby affects fundamental cellular processes, including proliferation, apoptosis, and differentiation. KRAS mutations have been commonly found in metastatic colorectal cancer (mCRC), lung adenocarcinoma, and thyroid cancer. The most common mutations are found in codons 12, 13, and 61. It has been found that screenings for both KRAS and BRAF mutations are necessary for more accurate identification of tumor cells that would not respond to anti-EGFR drugs.