Patients with non‑small cell lung cancer with the exon 21 L858R mutation: From distinct mechanisms to epidermal growth factor receptor tyrosine kinase inhibitor treatments (Review)

The most common oncogenic driver in non-small cell lung cancer (NSCLC) is epidermal growth factor receptor (EGFR) gene mutations, which are more common in Asian (30-50%) than in Caucasian (10-15%) populations. Exon 19 deletion (ex19del) and exon 21 L858R (ex21 L858R) mutations account for ~45 and 40% of all EGFR mutations, respectively. Moreover, EGFR-tyrosine kinase inhibitors (TKIs) may be more effective and improve the quality of life of patients with NSCLC more than chemotherapy regimens. By contrast, patients with the ex21 L858R mutation may have a lower sensitivity and duration of response to EGFR-TKIs as well as a shorter survival compared with those with the ex19del mutation. However, current guidelines classify ex21 L858R and ex19del as the same condition and recommend the same treatment strategy for both. Aiming for precision medicine, the present review introduces and compares different EGFR-TKIs for the ex21 L858R mutation to assess more personalized treatment options for the population with this mutation.