Long‐term response to afatinib in an elderly patient with uncommon epidermal growth factor receptor mutation‐positive lung adenocarcinoma

Abstract Epidermal growth factor receptor (EGFR) tyrosine kinase inhibitors are the standard treatment for patients with non‐small cell lung cancer (NSCLC) harboring EGFR mutations. Uncommon mutations, excluding exon 19 deletions and exon 21 L858R, comprise 7%–23% of EGFR mutation‐positive NSCLC. The treatment of uncommon EGFR mutation‐positive NSCLCs is controversial. Here, we present the case of an 81‐year‐old man who was diagnosed with lung adenocarcinoma cStage IVA harboring the uncommon EGFR L861Q mutation. The patient received oral afatinib treatment (40 mg/day). One month after the initiation of afatinib treatment, Common Terminology Criteria for Adverse Events version 4.0 grade 2 stomatitis was observed. It improved upon afatinib withdrawal. After 10 days of withdrawal, afatinib treatment was resumed at a reduced dose of 20 mg/day. Subsequently, the patient continued treatment with afatinib. A partial response to afatinib treatment was maintained for 49 months until primary tumor regrowth. Afatinib treatment was continued after disease progression, but the patient died of bacterial pneumonia 59 months after initiation of afatinib treatment. Several studies have previously reported a large number of compound mutations with uncommon mutations, and that compound mutation‐induced cells are most susceptible to afatinib. This suggests the efficacy of afatinib in clinical practice and that afatinib may be safely administered to elderly patients with appropriate dose reductions.