Afatinib treatment in a lung adenocarcinoma patient harboring a rare EGFR L747P mutation

Classical activating alterations including exon 19 deletions and exon 21 L858R point mutations comprise the majority of epidermal growth factor receptor (EGFR) changes in non-small cell lung cancer. Patients with these exhibit excellent clinical responses to EGFR tyrosine kinase inhibitors (TKIs). However, rare alterations including point mutations, deletions, and insertions occur and are associated with poorer responses to EGFR TKIs. Herein, we report an unusual case of a patient with lung adenocarcinoma with an EGFR L747P mutation (c. 2239_2240TT>CC, p.L747P) that was initially misdiagnosed as EGFR exon 19 deletion by amplification refractory mutation system PCR, leading to gefitinib as first-line therapy. However, both the primary tumor, mediastinal lymph node, and brain metastasis progressed after 1 month. A re-examination of gene mutation status by next generation sequencing revealed an EGFR exon 19 L747P, and this case then responded to second-line chemotherapy and third-line afatinib.