Abstract
Most patients with non-small cell lung cancer with common epidermal growth factor receptor (EGFR) mutations respond dramatically to EGFR tyrosine kinase inhibitors (TKIs), but data are limited on the response of tumours with uncommon mutations. We present the case of a 68-year-old man with stage IV lung adenocarcinoma with an uncommon EGFR mutation in exon 21 (L861Q). The disease progressed 2 years after he started erlotinib (150 mg daily). Using a transbronchial lung biopsy, we detected additional mutations in exon 20 (T790M) and exon 21 (L858R). He was treated with osimertinib (80 mg daily) and achieved a partial remission. This case demonstrates the value of repeating a biopsy after EGFR-TKI therapy in patients with uncommon EGFR mutations.