Durable response to osimertinib in an advanced lung adenocarcinoma patient with an uncommon EGFR T854A mutation: A case report

Epidermal growth factor receptor (EGFR) T854A mutation in exon 21 is an uncommon EGFR mutation in patients with non-small cell lung cancer (NSCLC). It is a secondary EGFR mutation after first- and second-generation EGFR tyrosine kinase inhibitors (TKIs). All EGFR T854A mutations were co-occurred with EGFR L858R mutation in cis. There is still no clear evidence to guide the therapeutic options for patients with both EGFR T790M and T854A mutations. PATIENT CONCERNS: A 60-year-old Chinese woman with no smoking history presented with a maximum diameter of 32.9 mm mass located in the right lower lung lobe. DIAGNOSIS: The patient was diagnosed with stage IVA lung adenocarcinoma with an exceptionally uncommon EGFR T854A mutation in exon 21 was detected concomitantly with EGFR T790M in blood by next-generation sequencing (NGS). INTERVENTIONS: The patient was initially treated with first-line afatinib. After disease progression, osimertinib was administered. OUTCOMES: Our patient exhibited a partial response (PR) to osimertinib with progression-free survival of nearly 8 months. CONCLUSIONS: Our study indicates that patients with NSCLC who are positive for uncommon EGFR T854A and T790M mutations might benefit from treatment with osimertinib.