Afatinib for an EGFR exon 20 insertion mutation: A case report of progressive stage IV metastatic lung adenocarcinoma with 54 months' survival.

Non-small cell lung cancers (NSCLC) harboring the uncommon epidermal growth factor receptor (EGFR) exon 20 insertion mutations are generally thought to be unresponsive to EGFR-tyrosine kinase inhibitor (TKI) therapy. Presented here is a case of stage IV NSCLC harboring an uncommon EGFR exon 20 insertion mutation that was maintained at minimal progressive disease for 54 months, with 36 months on the second-generation TKI afatinib. Contrary to the existing literature, the patient in this case demonstrated a long, durable response to the EGFR-TKI, which was exhibited by a long survival endpoint. This suggests that stability in clinical symptoms might be sufficient to warrant continuation of therapy.