EGFR exon 21 L858R as an acquired resistance mechanism to nivolumab in a lung cancer patient originally driver gene‐negative

The use of immune checkpoint inhibitors targeting PD‐1 and PD‐L1 in advanced non‐small cell lung cancer (NSCLC) has been one of the most significant improvements in recent years. However the resistance mechanisms of immune checkpoint inhibitors require further investigation. Herein we attempted to determine the possible resistance mechanism of nivolumab in a male smoker with advanced adenosquamous carcinoma. After experiencing disease progression on systematic chemotherapy, he was administered nivolumab as a result of high PD‐L1 expression. Larger panel gene detection was performed after the failure of nivolumab treatment to investigate the possible resistance mechanism and a new EGFR exon 21 L858R mutation was detected. After a achieving a response with gefitinib, the patient suffered a rapid relapse and died of tumor progression. This case represents the first time EGFR exon 21 L858R has been detected as an acquired resistance mutation to nivolumab. Patients with high PD‐L1 expression may exhibit a poor response to EGFR‐tyrosine kinase inhibitors. Large panel gene detection remains the optimal choice when confronted with drug resistance.