A rare EGFR exon 19 insertion mutation in metastatic lung adenocarcinoma: a favorable response to afatinib.

Epidermal growth factor receptor (EGFR) mutations like the common L858R and exon 19 deletions are well studied, but rarer mutations like exon 19 insertions have received less attention. This case report describes a patient with this uncommon EGFR exon 19 insertion mutation in metastatic lung adenocarcinoma. A 51-year-old male nonsmoker with metastatic lung adenocarcinoma and a rare EGFR exon 19 insertion mutation experienced disease progression on initial carboplatin-pemetrexed chemotherapy. However, treatment with the second-generation tyrosine kinase inhibitor afatinib led to a partial response, with significant regression of the primary tumor and bone metastases. This case highlights the favorable clinical response to afatinib treatment in a patient with metastatic nonsmall cell lung cancer harboring a rare EGFR exon 19 insertion mutation.