Lung cancer, which consists of over 80% non-small cell lung cancer (NSCLC), is the leading cause of cancer-related death in the world [1]. The discovery of the connection between mutant epidermal growth factor receptor (EGFR) and cancer cell response to EGFR-tyrosine kinase inhibitors (EGFR-TKIs) that led to development of EGFR-targeted therapy has revolutionized the treatment of NSCLC. During the last two decades, EGFR-TKIs have advanced from 1st and 2nd generation to 3rd generation agents represented by osimertinib (AZD9291). Because of its promising performance in clinical trials, osimertinib has been approved to treat NSCLC patients with EGFR activating mutations (e.g., exon 19 deletion and exon 21 point mutation L858R) as a frontline therapy or those progressed from 1st or 2nd generation EGFR-TKIs due to EGFR T790M mutation as a second-line treatment option [2, 3].