EGFR mutations and their clinical significance What is EGFR? The epidermal growth factor receptor (EGFR) is located mainly on the cell membrane and belongs to the receptor tyrosine kinase family. Mutations and abnormal expression of genes in the EGFR signaling pathway are present in many tumors, resulting in unrestricted tumor cell expansion and migration. Currently, molecularly targeted drugs targeting EGFR block the EGFR-mediated intracellular signaling pathway through different pathways, thereby inhibiting tumor growth, metastasis and angiogenesis, and promoting tumor cell apoptosis. Why is it important to test for EGFR mutations? EGFR tyrosine kinase inhibitors (mainly ERSA, Troche, and Kemena) are approved for the treatment of advanced non-small cell lung cancer and have been used in the clinical treatment of patients with advanced and post-surgical recurrent metastatic non-small cell lung cancer. However, the results of clinical use have shown that these targeted agents are effective in only some patients, and further studies have identified EGFR gene mutations as a necessary prerequisite for patients to be effective on such targeted agents. The clinical guidelines of the National Comprehensive Cancer Network clearly state that EGFR mutations, especially exon 19 deletions or 21 mutations, have an important relationship with tumor sensitivity to EGFR tyrosine kinase inhibitors. Therefore, the detection of EGFR mutations can guide the rational use of drugs for patients.