Rare case of de novo EGFR L718V mutation-positive non-small cell lung cancer successfully treated with afatinib

Since the FLAURA trial, epidermal growth factor receptor (EGFR) mutation-positive non-small cell lung cancer (NSCLC) has generally been treated with osimertinib as a first-line therapy. However, there is still insufficient data on the therapeutic efficacy of EGFR-tyrosine kinase inhibitors in NSCLC patients with uncommon mutations. Many of these minor mutations are resistant to osimertinib; one such mutation is EGFR L718V or L718Q (L718V/ Q), which may occur in combination with L858R. L718V/Q has been identified as a resistance gene to osimertinib when progressive disease occurs during treatment with osimertinib. Some reports have shown that EGFR L718V/Q with L858R is resistant to osimertinib but sensitive to afatinib. All cases of L718V/Q mutationpositive NSCLC reported in previous studies have presented with L718V/Q as the acquisition of resistance after treatment with osimertinib. In the present case report, we describe a rare case of NSCLC with de novo EGFR L718V and L858R mutations. Consistent with previous reports, the patient was resistant to osimertinib but responded well to afatinib.