Long-term response to osimertinib in elderly patients with lung adenocarcinoma harbouring de novo EGFR T790M: a case report and literature review.

Osimertinib is a potent and irreversible epidermal growth factor receptor (EGFR) tyrosine kinase inhibitor (TKI) that selectively acts on both EGFR-sensitive and EGFR T790M-resistant mutations. Patients with pre-treatment EGFR T790M mutations (de novo EGFR T790M) respond poorly to existing EGFR-TKIs, whereas osimertinib has positive effects. However, the safety data for first-line osimertinib treatment in patients aged >75 years are insufficient. We treated two elderly patients with de novo EGFR T790M mutations with osimertinib as the first-line therapy. We found that the first-line treatment with osimertinib was safe and resulted in a long-term response in elderly patients with de novo EGFR T790M-mutated lung adenocarcinoma.